bitcrushing contents of buffer~

I have some stuff in a buffer~, played back with groove~. Does anyone know how I can add a control to variably reduce the sample rate? There doesn't seem to be a parameter for this in any of the objects that work with buffer~ and I can't figure out how to achieve that effect by processing the MSP signal. The only thing I can think of is maybe using rampsmooth~. Any ideas are appreciated.

Thanks,
Zach