Finally finished my mod today. The most difficult and time consuming part of this mod is the preparation and etching of the flexible PCB.

Things needed:
1. copper clad laminate (pyralux) - flexible PCB
2. Copper tape
3. ferric chloride solution - for etching
4. Alcohol or acetone - to clean up pcb after etching
5. Water proof/permanent marker pen, tweezer, nipper/scissor, mobile phone pry tools, soldering iron, bla blah

Trial etching:

More pics: