A/B 2 into 1 mix volume pedal

[Chrisfromiowa]

Does anyone know of a volume pedal, ABY pedal mod that allows you to mix two signals into one output? I used to have an Ernie Ball stereo volume pedal that I used with one of the input signals put into the output to use as a mix pedal but I'm trying to do the same thing with only one amp, and someone stole my Ernie Ball. Thanks