OK.. just figured out a simple way to limit the pot's sweep to stay within the .5-2.5V range.
The equation to determine the resistor value you need on the ground leg of the pot is:
R / ( 500KOhms + R) = .20
R = 125KOhms
In this example, I am using a 500K pot and I want the lower voltage to be limited to 20% of Vmax.
I didn't have any resistors in the correct values to match my pots, but like any long term guitar player, I have a TON of old pots from past wiring projects. In fact, most of them are 250K and 500K (typical pots used in passive guitar wiring.)
Guitar Player's Solution:
So the solution is to use a 500K pot for the adjustment, and use a 250K pot on the ground leg to set the Vmin. 125K is roughly in the middle of the adjustment range of the 250K pot, so it's easy to dial in. This has the additional benefit that it doesn't rely on just math to get the correct resistance.
You can dial it in so that the sweep goes from .5 to 2.5V, or you can set it so the low voltage is .49V if you want an off without wasting any of the sweep range.
I'd say thats better than waiting a month for parts from China.