Maybe you could either use an expression pedal to do what you need instead or
May be try using a 25k Ohm pot, a latching foot switch wired to an audio jack in a small enclosure. Plug the output of the new box into the expression pedal input on the TF. switch the foot switch to change your wet dry mix to the pre adjusted amount of the pot. If you don't want to change the pot you could just cut the shaft off really short and don't put a knob on it.
Have fun. I have tried a simple momentary foot switch in the exp jack to change from 0 – 100 just for fun – works well.
