Change USB output from Main to Monitor for mix minus to computer

I need the USB output from Main Mix to be able to change to Monitor Mix.

Currently the output from the mixer to the computer is stuck on Main Mix but I want to be able to send a mix minus back into the computer instead so I can use the mixer on zoom without an additional audio interface. 

The use case is running in room FOH for a conference from the Main Mix output. Mixer is plugged into laptop for zoom presenter coming into the mixer on 7/8 and mix minus on monitor mix. I want mix minus to go back into the computer so that the presenter doesn't hear FOH mix. 

Looks like the only workaround I can see other than having a separate usb interface is run FOH out of monitor mix instead on prefade and the presenters feed from Main Mix through USB.

The downside of this is you miss out on post fader setting which would be ideal meaning you would need to mix both FOH and Monitor separatly.

Adding a software switch to change this setting would eliminate the need for a second usb interface receiving the monitor send.