Middle Click on empty lister background?

I've searched the forums and reread the Opus manual, and there doesn't seem to be any way to assign a command to a middle mouse click on an empty lister backgroud (no files or folders selected). I could do this through autohotkey, but I would prefer to keep the native Opus function for the MMB which is to perform a Ctrl + Click when used on files and folders. If I use autohotkey to reassign the MMB function in Opus (like closing the active tab in a lister), it will perform this at all times, when files and folders are selected, as well as on the empty lister background. Does anyone know of a way to assign the MMB a particular function when used on an empty lister background?

You can assign things to double-left-click on the background but not double-middle-click.

I figured it wasn't possible from within Opus. But I've written a short autohotkey script that gets the job done. It keeps the native single- click function of the MMB (Ctrl + click), but when the MMB is double-clicked anywhere in a lister, will close the active tab. Of course, you can change the DOpus command which is executed, but I chose to use it to close the active tab (Note: I created a hotkey in Opus to close the active tab using Ctrl + Shift + F9).

#IfWinActive ahk_class dopus.lister ~MButton:: If (A_PriorHotKey = A_ThisHotKey and A_TimeSincePriorHotkey < 400) SendInput ^+{F9} Return #IfWinActive