MOTM

At the risk of beating a long dead horse:
If the frequency shifter is to be in part digital, I assume it would 
include a PIC.  The potentiometer could be replaced by an encoder 
and the PIC could be programmed to interpret the encoder as a coarse 
control when turned quickly and a fine control when turned slowly.  
There could even be several scalings all based on the angular 
velocity of the knob.  The one large knob could be both the coarse 
and fine control.  
I have no idea of what this could do to the cost, but possibly you 
wouldn't need an encoder and could do the same thing with a pot.

I friend of mine used to run sound for a band I was in.  We used to 
feel sorry for him because the band members got the girls and all he 
got to do was pack up equipment, so we always told the girls he 
wanted a knob job.  Okay, Okay, I know.  But I'm just continuing the 
thread.