This would not fit inside my trackball.

Chopped it, soldered it, hacked it.

Dead bug style. I soldered the wires long through the holes to keep air space underneath.

The black 20 gauge wires soldered on top work with the female jumpers. These are for backup left and right mouse buttons if the Teensy is disabled.

This was designed split in the middle for hand comfort, like a split ergonomic keyboard.

The right half gets the trackball.

The first jumpers!

The first components on the board! The two mouse switches.

Remember the "3mm pin in 6mm socket" problem from the "Adafruit vs Futurlec Header to Header Grudge Match"? I found a simple solution. I inserted 24 gauge wire into the socket, cut it off even, then wiggle the 3mm pin along side of it. More pictures later.