Someone should build a lua tool for doing this in renoise natively, basically you can do grain manipulation (timestretching etc) on high enough pattern resolution (up the pattern length, bpm & lines/beat settings) and using the Sxx commands. There is a panning column for stereo fuckery and you can change the notes for different pitches of the grain -> then render the result to new sample.
If I had the coding chops Iād build this one myself 