A year or so ago I bought a beat up old bike at the local thrift store for twenty bucks. The gears didn't work, so I took the cables off, making it a one-speed. The front brake was busted, so that went, too. I found that if I rode the bike for more than a few minutes I got a stiff back from leaning forward all the time to hold the handlebars. So I used some scrap PVC tubing and a couple of PVC tees to make a handlebar extension. Now I don't have to ride hunched over when I'm doing some easy pedaling on a straightaway or downhill.
Step 1: Attaching the Tee to the Handlebar.
I took off the rubber cushions from the handlebars (A little WD-40 helps). Then I drilled a small hole through the handlebars about an inch from the end. I drilled the same size hole through one side of the tee fitting. Then I used a nut and bolt to attach the tee to the handlebar. It was a little wobbly, so I wrapped some electrical tape around the handlebar until I could just barely slide the tee on the bar. Make sure that the angle of the holes is the same for both sides. Mine is a little bit off, but it doesn't seem to make too much of a difference in the ridability of the bike.
Step 2: Add Some Tubing
I put some short (about 5 inch) pieces of tubing in the upright part of the tee. I was able to slip the rubber cushions partway over these pieces. Then I discovered I didn't have any more of the proper sized tees, but I had some smaller ones. So I stuck some smaller diameter pipes into the larger diameter pipes and stuck the smaller tees on top of them.
Step 3: FInish the Top Bar
I wanted to add one long piece of tubing to connect the two tees, but I didn't have one piece long enough. So I took two smaller pieces and connected them with another tee. Looks kind of funky, but it works.
Step 4: All Done
Here's a rider's eye view of the finished product. I did have to move the handbrake around a bit but it's actually very easy to switch from riding sitting up straight to grabbing the "real" handlebars.
Please note that I didn't glue any of the pieces together, just wedged them in good and tight. I wouldn't trust this for any mountain biking or anything strenusous, but for just zipping around on city streets, it seems fine.
I just had the bike out for a 4-mile spin and got a lot of strange looks.