In Macros, create a macro, call it "Prev Preset" or something.
Add an action to the macro: System / Preset preset
rev (use the "..." button to select the "Prev" special value)
Check the "Force State to" checkbox, and set the value to "On"
Edit your button, turn off all checkboxes except Momentary, which should be on
Add two actions:
System / Preset preset:x (where x is the preset you want it to recall when pressed
System / Macro off:y on:None (where y is the number of the macro you just created)
When the button is pressed, it will call up the desired preset. When it's released, it will trigger the macro which goes to the previously selected preset. The macro is necessary because preset actions don't have an "off" value - the macro kinda tricks the system into doing the right thing.
