These directions should work for any power connector that has the same basic design, if you make adaptations for differing sizes. See the second and third pictures in this step for a "before" portrait and a little bit of terminology.
This modification isn't destructive in any way, so it should be possible to restore your laptop to its original condition just by removing the pieces you've glued on. You can't use an unmodified power adapter once you've modded your laptop, but fortunately it's pretty easy to make the plug part, so you can make two or more spares.
Remove the battery before working on your laptop, and unplug the power cord.
Step 1: Materials
a soldering iron
You will notice in most of the following instructions that I only used two magnets. This is because during my initial build, I thought that two would be sufficient, and it was only when the whole thing was built and photographed that I discovered that they were not. Rather than start over, I simply used my Dremel to insert another two magnets, and the final design you see on the first page was born.
Depending on how many materials you already have, this should cost less than $30 for the whole project.
Step 2: Plug Wrapping
Cut a strip of copper sheeting and wrap it around the barrel, making it long enough that the washers will just barely slide on over it. Some trial and error will be necessary in this process. I eventually figured out that about three and a half wraps of sheeting worked best.
Step 3: Epoxy the Plug
Make sure that your magnets firmly contact both the washer and the copper foil. The magnets will be your new ground contact, so make sure that they have a good electrical connection to the ground cylinder on the original plug!
Use aluminum foil and rubber bands to make a seal so that the epoxy doesn't run off the edges. Prop the plug upright, and carefully insert epoxy in the spaces between the magnets. You don't want to get any epoxy on the top faces of the magnets, and you don't want to get any in the hole in the center. But you do want to fill the spaces between the magnets with a little pool of epoxy, bringing it almost flush with their tops.
This will seem obvious in hindsight: don't use an iron implement like a nail to apply the epoxy.
Step 4: Solder the Socket Electrode
The strip should be slightly narrower than the ground contact inside the Thinkpad power socket, otherwise it won't have such a good connection. Do some test fittings on the laptop and bend a right angle into the strip so you know where to solder it. The strip should go all the way to the bottom of the socket. You can see that I folded over the end so that it fits more tightly.
Then, fire up your soldering iron and solder the strip to the washer. I found that the best soldering strategy is to heat the washer with the iron on one side of the strip (use a small blob of solder to increase heat conductivity), and have fresh solder ready to flow under the strip on the other side.
Step 5: Install the Socket
This is a good time to give it a try. Gently work the electrode into the socket until the washer is flush with the surface of the laptop. If you have a multimeter, see if the washer is connected to the laptop's ground. The outer metal bits of most of the connectors on your laptop will be equivalent to ground, so check for continuity with those.
Once you're satisfied that the electrode is making contact, epoxy the washer to the face of the laptop. Make sure it's centered and even. It's not completely impossible to remove it once you've done this, but it won't be very easy .
Step 6: Cut Rod to Fit
If you have a spring that fits perfectly in the hole already, then you can skip this paragraph. I couldn't find a small enough spring, so I modified a spring from inside a pen. Snip a short segment of spring from the pen, and then use a pair of needle-nose pliers to tighten the loops. Keep tightening and fixing until the spring is small enough to comfortably fit down the hole in the plug. Don't force it -- you never know when you'll want to take it out again.
Now you want to adjust the length of your aluminum rod so that, sprung, it is slightly too long. Put the rod in the chuck of your power drill and run it against some sandpaper to wear it down quickly. Start with coarse sandpaper, and finish off with fine to ensure a nice finish. Go through a bunch of iterations to make sure it's perfect. Go through some rounds of testing -- when you attach the plug to socket, does the rod get pushed back against the spring? Do the magnets still hold them together?
Once the rod is the right length, wrap a strip of scotch tape around the part that sticks out, so that only the tip is exposed. This will help prevent you from touching the powered-up rod to the ground washer on the laptop. You can put as many layers on as you want, as long as you don't exceed the size of the hole in the laptop.
Step 7: Done!
Well, hopefully anyway. Put the battery back in your laptop, try out your new plug, and see if you get power. You might have to fiddle with the length of the rod, or smooth out the surface of the magnet/epoxy combo. If you're not getting power, try testing the continuity between some of the washers on the plug, and the ground point on the laptop. If there's a good connection between those, then the problem must be the rod/post connection, so check on that. Make sure to clean the surfaces off so there's no grease getting in the way.
Enjoy your new freedom to trip over your power cord!