If you select stereo mode instead of surround when you use the additional speakers that will shut off the center and rears. I will leave the sub on though. If the sub has speaker terminals on it you can connect it in parallel to the front A speakers and set the receiver speaker menu to front large, no sub. Then it will turn the front speakers and sub off when you turn off speaker A.
The other solutions are to replace the receiver with new one with 2nd zone capability or add an additional receiver or integrated amp just for the remote speakers.
Thanks for the help! I am going tell him to try stereo mode when he is in channel B.