Realtime this isn’t supported for internal instruments.
If you desperately need something for one or two instruments, you could try this tool which you can control at least the pitch of an internal instrument, but do know that this is not running realtime but in the UI thread (also see the link in the top of that topic). So far i could do decent handling of pitching a few instruments, but i have a reasonably fast pc with a quadcore cpu.
I suspect the mod wheel and pitch wheel to turn applicable to internal instruments in one of the future major updates of Renoise. That’s also the reason why i write those lousy tools:to be able to ditch them again as soon as stuff is embedded natively.