The only problem I see is if the injector or some part of the line gets clogged, kinked, etc. In that scenario you have pressure in the line but no (or not enough) alcohol being injected. Pop goes the motor o_O

I would wire up an EGT and use that in conjunction with the pressure signal to determine if boost should be turned on. This way if something happens and EGTs start to rise above a certain temp boost will be cut.

I'm not sure if there are any other signals that should be monitored in order to determine if safe conditions are met in order for the alcohol to be injected.