Would it be possible to add switches to the ioptron CEM120 driver to switch on PEC playback as well as start a PEC recording.
It could be difficult though as the driver would have to disable them for EC and EC2 mounts because they don't have (or need) PEC

According to this doc www.ioptron.com/v/ASCOM/RS-232_Command_Language2014V3.pdf the commands are as below.
Command: “:SPR0#” or “:SPR1#”
Response: “1”
These commands set the status of PE recording. “0” stands for stop recording PE, “1” stands for
start recording PE.
Note: This command only available in non-encoder version of equatorial mount.
Command: “:SPP0#” or “:SPP1#”
Response: “1”
These commands set the status of PEC playback. “0” stands for PEC playback OFF, “1” stands for
PEC playback ON.
Note: This command only available in non-encoder version of equatorial mount.

Perhaps check :MountInfo response.. maybe it is sufficient to know which is which?