I believe most expression pedals use a 3-conductor connector, where one is power from the master device, one is ground, and the third is the output voltage.
Basically just a potentiometer connected to those 3 lines, AFAIK.
But the problem is the Minibrute doesn't output power from its jacks. So you'd need a little adapter, though that would actually be pretty trivial.
I don't know off the top of my head what the exact connections are, but basically you'd need to have an adapter that connects the sleeve connection on the minibrute side to the ground connection of the expression pedal, and the negative/ground side of some power supply, could be just a 9v battery even, I think. Then the positive end of the power supply goes to the power connection on the expression pedal. The output of the expression pedal would wire to the tip connection into the Minibrute.