The pitch-shifting approach might be ugly just because pitch-shifting brings the formants right along with it. Anything more than a few semi-tones will start to get all chipmunky. You might be able to do some FFT stuff to preserve the spectral envelope, but I still don't think you'll get a convincing range.

The VSTi stuff would really depend on the plugin. It will generally be a pain in the ass trying to get a synth to do something it isn't meant to do. Personally, I think it would be more fun to just try and make your own synth in Pd that handles [fiddle]'s data just the way you want it to. But that's just me.