Question Stereo to two mono

[pipster]

I have a 4-zone multi channel amp. The first 3 zones will be wired as normal stereo in three different rooms. But the 4th zone I want to combine both the left and right channels into two independent mono signals (for two different rooms - basically I need 5 channels but only have 4). Can I series wire these speakers and bridge the left and right channels on the amp (i.e double impedance but double the input signal)?