I have several of these fobs. CM108 and open to mods.
Looking at the board carefully, it looks like the mic tip and ring are wired together and removing 0-Ohm chip resistor R6 opens the 4V mic Vbias line from CM108 pin 25, leaving mic T+R pins connected to CM108 MICIN pin 27 through a chip cap. Mic T-R pads are on J3 on the red LED side of the board if the jacks are removed.I just confirmed R6 does indeed remove the 4.5V mic bias.
Duane KA1LM