If you want to do it without extra gear then Source Audio’s Dual Expression plugs straight into the control port.
Do you already own a MIDI switcher and have something that can act as USB MIDI host? If not, you’ll need to get one in order to access presets 7-128.
I’d recommend getting the SA Hub and a Morningstar controller.
There are other options from Disaster Area which do simple preset switching, a few programmable MIDI commands and act as a host.
Both the above allow you to plug any expression pedal into the controller and send signals to the C4.