Yes. You will need to know what resistance the thumb controller is, so you can get a digital pot of approximately the same value.
Using a diode, capacitor and resistor sure seems easier to me than ordering a digital pot and waiting for it to ship to you. You can probably do it with $3 of components from Radio Shack.
i guess i put it on 20K since that is the closest setting to 10K
you do it with the board powered off where by it uses the multimeter power?
If I was messing with it I would go with Richards suggestion, the pot is just acting as a voltage divider, you can take a pwm signal, run it though a low pass filter made out of a couple passive parts (that yes radio shack sells at your local mall) and just stick it where the middle pin is and the controller would be none the wiser