4 channel bridged

The Only speakers running off my Head Unit are my woofers in my rear backseat, and i want to give them more power by wiring them to my HU differently. I was thinking about how i can bridge a 4 channel amp to just two speakers by connecting the negative speaker wire to a negative of one channel...

I want to bridge my 4 channle amp but I want to use it for left and right instead of front and rear I'm only concerned about the front stage with my amp and I'll use the the rear output of the radio to power my back door speakers, how would I do that since 1/2 bridged has a left and right and so...