There is no way to wire a 4 channel amplifier into one channel unless the amp is designed from the outset for it (read one hella pricey amp). I can't remember actually coming across one in the last 20 years for that matter. Your 4 channel must be one of the HC series amps, if it is stable to 1 ohm on a set of bridged channels, that's great, use the amp in 3 channel mode, 2 channels to run the front or other speakers and the bridged channels to run the subs.