Step 1: Remove the Top Half
Once the screws are out (keep them organized: they are different sizes), the white shell will slide off the battery casing and electronics. Watch that you don't catch the power cables which inexplicably cross the circuit board. Already at this point, I've found a number of unusual design decisions that I'm really hoping won't show up in the Roomba itself.
Step 2: Exploring Time!
I'm hoping to later take the component values and find out how to make one of these for myself.
Step 3: Serious Business Time
Second picture shows the stuff I gathered:
-Mini SPST Momentary push switch
-heat shrink tubing
-light gauge braided wiring
Step 4: Dremel
I love this bit for my Dremel. It cuts really clean holes in the plastic items that I've messed with before. Just don't poke it into your hand, because that really hurts.
Step 5: Wiring
Cut into the power button's lines (white/black) and tap your new button in parallel with the first. Make sure your new lines are long enough to get the cover back over top of the wall, but not so long as to bunch up or pinch when the cover is in place.
I used a spot of packing tape to keep those previously mentioned board crossing lines out of the way of catching on the switch terminals.
Step 6: Sweet, It Worked.
I went ahead and put the fastening nut on top of the cap as it made everything much more stable and even added a not-too-bad trim look. Now I can turn the wall on and off with the toe of my shoe, a long stick, or whatever comes to hand. The switch seems to have a good level of responsiveness and I haven't noticed any problems with the function of the wall.