I don't think there's any way to piggyback one decoder with another decoder, and almost certainly not with Railpro. They don't communicate in a language that is even remotely similar. If you're wanting the control that Railpro has to offer, Ring now has recordings of several variants of Alco's which should be getting released this year. ESU has more recordings, yes, but they have also been at this much longer than Railpro has.
-Kevin