It depends on your Footswitch. You would need a MIDI Footswitch capable of sending 8 different CC values... a device like the old Yamaha MFC10 MIDI Foot Controller would be ideal as it featured 10 programmable switches and options for multiple sweep pedals...

MONTAGE/MODX Scenes are selectable directly or via MIDI:
1) pressing the dedicated front panel [SCENE] buttons, 1-8
2) sending a designated CC# and value (or a System Exclusive Parameter Change message) via MIDI

You can choose a MIDI CC#:
In [UTILITY] > “Settings” > “MIDI I/O” > Scene CC
Say you select CC92
Any value sent on Ch1 within the range would cause the Scene to change
Scene 1 0-15
Scene 2 16-31
Scene 3 32-47
Scene 4 48-63
Scene 5 64-79
Scene 6 80-95
Scene 7 96-111
Scene 8 112-127

Options include:
_ Smart Device (iPad/iPhone) connected to the USB “To Host” port.
_ External MIDI device capable of sending CC# plugged into the 5-pin MIDI IN.
_ Scene changes can be automated by the internal Sequencer:
1) create a CHAIN. Touch “Play/Rec” > “Pattern” > “Edit/Job” > “Chain” ...(First column is the Measure number, second column the Scene).
2) Scene events can be documented to the MIDI Song

I'm using a Keith McMillen 12 step to change scenes on Montage.