The ASCOM driver doesn't use the HC sync command at all for the StarSense HCs. Instead it applies an offset in the driver to do sync independently of the HC. IIRC there is something similar in the INDI Celestron GPS driver which could be used.
I'm not in a position to do any INDI development at the moment but if someone wants to have a go... The 'm' command identifies the HC type, NexStar or StarSense. If the command fails it is a NexStar.