Id get hold of a "mousepressed" program and edit the startup-sequence to work with the inputs from this. I use this on my own Amiga.
System:c/mbpress
set ANSWER $RC
If $ANSWER EQ 0 ;no mouse button pressed
Run USB software
;
; Below show how this program become a multi selection
; $ANSWER EQ 1/2 = left/right mouse button
;
; Else
; If $ANSWER EQ 3 ;middle mousebutton
; Run other program
; Else ;any left or right mousebutton
; Run a third program
; EndIf
;
Endif
