You might be able to use something similar to the volume pop-up sample on the two way training video (at 1:28:15), but rather than have a volume display you could have the pop-up contain all buttons you need to control the volume in all zones. Set the pop-up and all it's buttons to be visible and each time a button is pressed, you could run a system macro to delay for say 10sec. After the 10sec is up for the last button press then you can clear the flag and the pop-up should disappear.

Check this thread for more info on how to setup a pop-up with a delay.

[Link: remotecentral.com]