I've posted this question on the AutoHotkey forum, but in case anyone here knows the answer....
This works, but only when assigned to a Right Button single click.
I have no idea how to assign it to an Alt-LeftButtonDoubleClick.
I could live with an Alt-Rightclick, Ctrl-Rightclick, or any combination of Alt/Ctrl/Shift-Rightclick/Middleclick. but when I try any of these:
either the new window doesn't open, or nothing works.