how remap R3 from PS4 jdm-055 to a back tact switch!?

[NOTnuk]

Hello everyone, I added 2 back button to my ps4 controller with a flex remapper.

The flex does not have the R3 option, so I would like to know if there is a way to connect the rear button to the controller PCB somewhere to get the R3 input.

I tried some point where the R3 button is connected on the pcb but it doesn't work. 

if someone maybe can show me with an image would be lovely.

[RDC]

There are 4 solder joints under the R3 button, 2 are 3.2v, the other 2 are the R3 button line. Just pick 2 that are opposite corners from each other, like the top right and the bottom left ones, and there you go, duplicate R3.