Disconnect my automatic shifter linkage, connect some sort of linear actuator or servo to the transmission. Hook this up to an Arduino. Hook the Arduino up to power, plug in a couple buttons, and do some programming. Design paddles, put buttons + paddles on steering wheel, bam. Flappy-paddle-shifted 4T65e. Right paddle would move 1>2>3>4>N>R>P left paddle would go P>R>N>4>3>2>1. Slightly unintuitive, but that's the order the transmission goes in. Anyone know how much force is usually needed to move an autobox like this between gears? I can't tell if the resistance when I do it from inside the car is resistance from the transmission or resistance from the linkages in the steering column.
I'd also have to re-tune my transmission to disable all automatic shifting (change the upshift points to something above redline, downshift points to 0rpm, disable kick-down, torque converter always unlocked except for in 4th [overdrive]), but I could get a decent simulation of a flappy paddle gearbox, and wouldn't have to worry about the damn thing hitting 2nd at inopportune times while autocrossing.
Thoughts? Would make a fun project to keep me busy.