I came upon a very nice mouse for the shifter. I already had the PS2 version, but ordered the USB version for the vehicle. It was $20.
They were also available on Amazon, but, when I went to provide that link, they're "not available" there (I had searched for "finger mouse").
Mine isn't installed yet, but I have used it for testing. It isn't great for use with a keyboard -- you have to take the mouse off your finger to type -- but I think it'll work fine mounted in the vehicle. My plan is to disassemble it and mount it right on the shifter.