[Electronic M]

Another possible temporary option would be to get one of those giant, old, high-watt, ceramic, wire wound resistors (I used to have a bunch, but have not seen them since the last move) some had a side of the wires exposed and a slidable center tap thus makeing them a (very annoying to adjust) slide potentiometer.

EDIT: There is a surplus store in Orlando called Sky Craft that has some of the type I mentioned above and may have the right value with an adjuster. These resistors have no insulation on the center adjuster so you would have to jury rig one or keep the set off when adjusting it.