OK the X-keys pro has 2 layers, you might be able to set one of the pedals to toggle layers for you (it can be a held or toggled switch)

otherwise surely you just bind RALT RCTRL and RSHIFT to buttons ont he xkeys?

I have shift, ALT and Control bound to the bottom centre row of my X-Keys Pro, this lets me use the 2nd from top row for my druids heals each key is a different char and the modifiers are the different spells.