You could do it using a mouse click and AutoHotkey.
See the help for #IfWinActive
the class names for Explorer folder windows are
CabinetWClass and ExploreWClass.
You can group them together to do one test as in
Ask for help on the forum to fix it up a bit. You don't want the clicking to be constant. You'll have to figure out how to tell if you've already adjusted that particular window etc..
GroupAdd ExplorerGroup ahk_class CabinetWClass
GroupAdd ExplorerGroup ahk_class ExploreWClass
#IfWinActive ahk_group ExplorerGroup
MouseGetPos,X,Y ; save mouse cursor
Click,25,40 ; experiment to get the x and y relative to the window frame
; it shouldn't vary all that much with the screen res.
MouseMove,%X%,%Y% ; put mouse cursor back
AutoHotkey is free. Plenty of help on its forums.