If you want a "return to center" spinner then do this (or something like it).
Get yourself a cheapo 270 degree PC steering wheel (the cheaper the better).
Tear it up, pull the wheel off (nicely), and add either a stereo knob (easiest method), or a real spinner knob to the existing return to center pot.
Wouldn't that be defeating the purpose, since he wanted to use it as a cheap alternative to a wheel for playing Outrun & others. If he has to go out and buy a wheel, why couldn't he just keep it intact for driving games, I think it will yield much better results than a hacked return to center spinner.
Not knocking your idea Paige, it was a good one, and he did ask how to build one, just think using a steering wheel would work much better for the driving games he's referring to.
On a side note, was there any games that used a return to center paddle?