Well, if that's true, which would be odd that they are wasting CPU time to check for a fan to be on that they did not turn on (avoiding proper coding technique discussion), then you could route your own power to the fan (annoying) and a few diodes later then fan would be under your control without letting the ECU know about it.
Then again, that's all probably a huge waste of time and you should rather implement an engine misting feature which lightly mists the engine to shed more heat
