The easiest way would be using the command line with NirCmd
A .cmd file with this command in a directory in your Path should do it:
nircmd.exe win close stitle %1
(of course NirCmd.exe should also be in the path to keep it simple)
Say you named it cl.cmd and the inactive window had a title EditPadLite
then typing cl EditP <Enter>
or as much of the title as needed to identify it by the starting characters, and NirCmd should close it. Otherwise you'd have to collect all the windows on the system and sift through them to avoid making the window the active window to get the info. There are lots of hidden windows that you really don't need to deal with. Just unnecessarily complex. If you absolutely hate using a command prompt you could make an alias for FARR using the $$1 placeholder for the command line param with the partial window title, and use the alias instead of the .cmd file.