The problem with clicking someplace outside the window you are working on is that you will change focus, so any <Enter> or <Return> at that point wouldn't happen in the correct window, at least not with only a few lines of script.
I use mouse rocker combinations (hold down one button and click/doubleclick/triple click the other, hold down one button and click the scroll wheel, hold down one button and roll the scroll wheel) for a variety of things: cut, copy, paste, delete, return, escape, close tab.
Each assignment is a few lines of Autohotkey script. I use LeftButton/ScrollDown for <ENTER>, maybe that sort of thing would work for you adjusted to the trackball. A snippet of code I lifted/copied/adapted from someone/someplace else:
~LButton & WheelDown::
GetKeyState, State, WheelDown
If State = U
SetTimer, RemoveToolTip, 2000