Someone actually sells PDA styluses that fit this description. Squeezes
on your finger tip with a little blunt pointy thing to poke the PDA
with. Google turned up http://www.man-machine.com/finger_stylus.htm

Thought it was a bit geeky for the office but here....

Ray Lovinggood wrote:
Sometimes, I find tapping on the screen of a PDA in
the cockpit a bit of a nuisance.

How about a banjo pick? I've rounded up one from a
coworker. Here on the ground, it works just fine.
Just slip it over my index finger and, voila, an instant
long fingernail. Easily controlled, even more so than
the stylus.

Ray Lovinggood
Carrboro, North Carolina, USA