I wish I could give you a definitive answer to that mate

Given that the wasted spark fires so late when you are on boost (ie its at its most retarded point), its perfectly possible it could do so while the inlet valve is open, you will need to actually look at the point in the cycle you first see lift on the inlet cam, work out how many degrees of ignition timing that equates to, and then look on your map to see if that is an issue. (event then if you havent got perfect valve seal, it may still get enough fuel from the nitrous kit past to be a problem)
Can you not just go to a 4 coil setup to be sure?

Lead_foot, he ISNT joking, and its not a 50 quid plenum he is risking its an MIS one!