Way back I asked TA if he could change the 3 channel mapping to I/O pins to match up to a 2 standard channel FET+1, but it didn't happen. If he would have put the FET on pin #6 and the 7135 bank on pin #3, it would have been no problem.
So for what you got, pin #5 is the single 7135, pin #3 is the FET, I believe... I think this is the same thing Lexel asked just up above?
Even in my small OTF M3 16340 light, I was able to use a TA 15 mm board, using 3 7135's in the bank, but kept the original driver as a contact board, and mounted a filed down TA 15 mm slanted, at a angle.
I haven't tried doing what you are asking, and it's certainly possible with a little tweaking. It would be much easier now in NarsilM, since NarsilM has much more flexibility from the prior Narsil versions. I don't think Lexel knows code/programming enough to make and test the changes, though he knows a lot about the MCU and hardware designs, etc. I didn't hear back from him bout what I posted above, so I guess it didn't work out.
Boy, I could get this working, and I'm sure it will help out more than just you, and I can even find usage for it, I'm sure. Problem is time, with so much going on right now with the Q8 and GT projects, plus other stuff on very limited time availability.
How about if my next weekend, I can get to this, maybe have a tested solution. Do you have the capability to re-program the board, download a HEX file?