I think I didn't explain my concept very well, judging from the reply below.  Picture two miniature toggle switches mounted side-by-side against each other.  The toggles are so close together you can easily move both together - in fact it would be difficult to move one without moving the other.  Then put nicely-shaped knobs on the end of the toggles and it even looks like a singe knob, but split down the center.  This is the system used by most certified systems, including all the S-TEC autopilots I've seen in light aircraft as well as in heavier iron, as Skip mentioned, and of which someone posted a picture.  What I'm proposing is instead of using center-off double-throw switches, use single-throw switches.  Of course you could only trim in one direction.  Then install another pair on the front of the stick that actuates the trim in the other direction.  One pair of switches in the rear of the stick, actuated with a downward motion, produces nose-up trim while another pair of switches mounted in the front of the stick, also actuated with a downward motion, produces nose-down trim.  Could also be pushbuttons, I suppose.  2 pairs of switches, 4 total.  The intent is to use the digits that are "unloaded" and available - your thumb when pulling back on the stick and your index finger when pushing forward.