First of all: This is not a three-way switch. To do that: just use Button Groups
This is different from using button groups in that each value continues to send out while the user continues up or down. This is a variation on the Relative Control (sends 127, 64 and 0, usually).
Set it up like this:
Note: Knob-etc = Knobs or sliders or crossfaders or XY pad dimensions
Set a supercontrol Knob-etc. (or slider/crossfader)
Make supercontrol of type (or subtype) relative
Supercontrol options: supercontrol is sequential
Give it three subcontrols (Knobs-etc.)
Set the supercontrol to have "sequential" subcontrols (options for super)
should switch between them.