Dual concentric pots also exist. The only ones I found easily are 500K but should work. The inner shaft is small and goes through the larger outer shaft, allowing each section to be adjusted independently. They are available from many guitar part vendors, along with suitable knobs. Fits in place of the current control, wired up the same. I could not quickly verify that they have an audio (logarithmic) taper but even if they don't some faking can be done with a couple resistors.
Just another option.