Ok, so when you spray you are supposed to pull out a bit of timing. Instead of making a "nitrous only" tune with that timing permanently removed, what about using the "IAT Spark Advance Correction" table? Here is my idea...
I will mention for starters that this car is never driven in temps less than 50 degrees. This is a 1991 Cutlass Supreme with a 2002 L67 3800 SC V6.
So figure out what value resistor is needed to tell the PCM that the incoming air temp is below a certain value, say 0 degrees or less. Then, use the normally closed contacts of a relay to utilize the factory IAT sensor, but then energize the coil to switch to this specific value resistor when on spray. On the IAT Spark Advance Correction table, at 0 degrees and below, remove the necessary timing for nitrous, like -4 degrees.
Is this a silly idea, or would it actually work? Are there any issues with doing something like this; like would this affect any other areas of the tune?