I'm helping somebody who wants to do the same thing. I could not find any valid termination that had anything to do with a User Button, either, but here is a solution that seems to work with my test setup (your mileage may vary):
Brain:
Input X -> No Op -> OEMTrigger X
OEMTrigger X (Config -> Ports/Pins, Input Signals) was Enabled and Emulated, no actual port/pin or hotkey information configured. The action for OEMTrigger X (Config > System Hotkeys) was configured to be OEM Code 301, which runs the current trigger macro. The trigger macro was setup as Scott said, using a macro in the Init String (ie. M1000 in his example) to SetTriggerMacro() the "working" macro (ie. M1001 in his example)...
I hope that helps,
scott