Here is where this guide earns it's 'Very Difficult' rating.

These pictures where taken with a Celestron Deluxe Handheld Digital Microscope. And that's 26 AWG magnet wire.

The first picture shows the pinout on the connector. I have labeled the traces on the second picture in case you want to tap them instead. It might be easier.

The third picture shows the second time I tried this mod and bridged 2 of the connector pins. I couldn't clear it up and attempting to remove the connector led to it's accidental destruction. I probably could have gotten a replacement connector but I just folded back the flex cable onto a piece of double sided tape and soldered right to the traces. The original side switches work fine this way, but it's not quite as neat a job as I would have liked.

The third time, I ended up using 35 AWG magnet wire. I tried first with the larger wire, but messed up the connector again and it had to be removed. After that, I was still having trouble soldering to the pads on the PCB but the smaller wire solved that. The 26 AWG is actually wider than the gap between the pins on the connector and this is probably what caused all the trouble.

Update: I haven't found the exact connector, but I did find a compatible one at Mouser. It's a .5mm 4 pin Hirose FPC connector (Mouser Part Number 798-FH34S-4S-0.5SH50)