Well,if it cannot be done that way,could I maybe use RP1000 as foot controller for the Guitar Rig?
EDIT:I tried using RP1000 as Guitar Rig foot controller,and it sounds great for me,so anyone who has Digitech RP stuff with in-built whammy and Guitar Rig can play MOTP without any problems.
EDIT2:I also tried to use Line6 UX1 as MIDI interface,and it also worked,so now I think that every MIDI interface that can connect your PC,guitar and amp at the same time will do the job.