So.. the deed was done :)
Took me a while to calculate the ramping steps for the two channels, but for anyone interested swapping in an XP-G2 (1 + 3 7135's ~1400mAh) here are the PWM levels:
#define PWM1_LEVELS 1,1,1,1,1,2,2,2,3,3,3,4,4,5,6,6,7,8,9,9,10,11,12,13,15,16,17,18,20,21,23,24,26,28,29,31,33,35,37,39,42,44,46,49,51,54,57,60,63,66,69,72,75,79,82,86,89,93,97,101,105,109,114,118,123,127,132,137,142,147,152,157,163,168,174,180,186,192,198,204,211,217,224,231,238,245,252,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255
#define PWM2_LEVELS 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,3,6,8,11,14,16,19,22,25,28,31,34,37,40,43,46,50,53,56,60,63,67,70,74,78,81,85,89,93,97,101,105,109,113,118,122,126,131,135,140,144,149,154,158,163,168,173,178,183,188,194,199,204,210,215,221,226,232,238,244,249,255
#define PWM3_LEVELS 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
These are the PWM levels considering no further modding would be done, PWM3_LEVELS being the FET.