Q: All the other buttons have screw in posts or a 20-pin connection. How can I get buttons for Touch Pad, L3 and R3?
A: There are 2 ways to get to the touchpad, L3 and R3 buttons.
1. Soldering to the TP key, L3, R3 and Gnd in same section using a ground daisychain and signal wires with .110 quick disconnects
2. If you have the UFB with headers, you can get a JST PH 2.0mm 4-pin connector with wires and splice wires to quick disconnects to a button. Be sure for the 4th wire you splice in a 3 quick disconnect daisychain
Digikey, eBay and many other electronic suppliers have these connectors. You can solder the header and hook up the connector as well