Eagle,
Not sure I understand the question. Are you saying to use oxygen INSTEAD of nitrous or WITH nitrous?
Adding more oxygen with the nitrous will make it leaner.
From what I have read about the problem of nitrous systems on boat motors (and a few people have tried it) is the fuel enrichment needed at the same time. It needs bucket loads more fuel when the nitrous is switched on. If the motor doesnt get the fuel, or not enough, it goes lean and BANG in a most spectacular manner. I asked Jim Auguston (SP?) about the system he was developing for K&B 67's, he said according to his dyno the engines made 60% more power than with methanol. But he killed a LOT of 67's and I dont think it ever made it to a boat...
Ian.