What I have done in the past, is replace the encoder with one that includes BLDC commutation pulses, you need to know the pole count to obtain the right one.
This changes the motor from 3ph sinusoidal to BLDC.
I used to get them from Renco before Heidenhain took them over.
But there are other sources.
BLDC reputedly offers slightly more torque than sinusoidal.
This was not intended for A-B however.
The original Fanuc has proprietary method of commutation.
Al.