It's not all that unusual for the lighting system to be run by an ECM, BCM, or any other type of module for that fact. Nissan has actually been using multiplexing modules for quite some time. Door lock modules in the driver's door come to mind in the Maximas. A lot of manufacturers use modules for lighting (delayed domelights, delayed headlights, automatic shutdown). I blew the parking light input on a BCM in like a a 97 Buick once (lucky it was my buddies grandmother's car). Took me 5 hours to find the blown transistor. That really sucked. Kind of the reason I don't know if I am willing to rip that IPDM box down to see what it looks like in there. But, there is usually a chink in the armor somewhere. This one is just tougher because it's the combination of both the head light and fog light switches being used by the BCM to signal the output from the IPDM through a multiplex channel. I think all in all, if the only interface point is after the relay, then it would probably just be easier to put in auxillary lighting