I have an FS-6 too, tried that first. If the function does not support a momentary switch in the board's operating system, changing the setting on the pedal won't help.

You have to use MIDI messages (with an "off" message upon release as permitted by the Midi Solutions module.)

If you're really good with electronics, you could build a generic switched circuit that closes briefly on press, then reopens, and closes again upon release. Hard to believe Roland, Boss, Korg don't sell a switch like this either!