Well, there might be, but it's kinda outlandish. Are you able to determine which sound comes out first? While I hear the echo, I can't tell which is first.

You could actually get a separate audio delay line for each of the two channels. It's not likely to be inexpensive and it depends on Zone 2 being ahead of the surround zone... but it's possible.

That trick with the Pioneer and Speaker B requires going into all channel stereo. Otherwise you have no center channel on Speaker B and, for instance, singers won't be there! But doesn't the Pioneer do almost exactly what you want? It even keeps your client from having to mess with surround modes.