jeffn1
2
I hesitate to respond, because I do not have much to offer. But, since no one else has responded, I’ll try. 
I guess I would want to know what the “old-school” footswitch is? What type of data does it send out?
There are threads about scripts to convert PC messages to CC messages:
(But maybe now it can be done without scripting?)
Within GP, you can use the GP midi filter to convert cc messages to PC messages:
Sorry if this is not helpful, but I figured I’d give it a shot.
Jeff