Made this today, it works pretty great! Try it.
Cool. So it has a potentiometer? Do you know what value? Most exp pedals are 10k or 20k linear but of course you can use a higher value pot with a resistor to get in the ballpark.Most damper pedals are just momentary switches, and some that do half-damper use one or more resistors so the output jumps up in steps, but for the DP-10 they just made it the same as an expression pedal.
Or if not you can just reverse two wires inside to make it work in the direction you want.Some effects units can be set to interpret the pedal in reverse, so 0 is 100 and 100 is 0.