Mike, it's possible even with amps that don't have built-in provision for bridging, but it would take a lot more than just wiring. What is involved in bridging two amp sections is sending the voltage from the positive terminal of both amps(instead of positive and negative of one amp)into the terminals of the single speaker. Now if this added those two voltages together, then the power would be theoretically quadrupled(not just doubled)because pursuant to one form of Ohm's law power is equal to voltage squared divided by resistance(P=V(squared)/R)so twice the voltage equals four times the power(losses make it more like three times in practice).
The problem is that with the majority of amps, which don't have bridging provisions, the voltages of the two amp sections are in phase with each other and would in effect run head on into each other in the speaker and cancel out, not add together. One of the amp outputs would have to be inverted in phase 180 degrees with respect to the other amp so that in effect one would be pulling in the same direction as the other was pushing and their voltages would then add. There are bridge converters, adaptors,inverters, etc. around or plans to build them.
