you do not need to run a P8 ecu at all. that may be the easiest way, but it's certainly not the only way, or probably the cheaper way.

all you need is another amp (or replace the single one with a twin) to run in wasted spark mode (i.e. 2 plugs get a spark at the same time, but only one cylinder is ready for firing). you then need some way for the pulse from the ecu to the original amp to be split into 2 and sent to the correct amp for firing of the right pair of cylinders. this can be done with a microcontroller sensing the pulses from both the crank position sensor ad the phase sensor, but they need somesignal conditioning first.