"Subst Drives" Not Recognized by Tools Menu

I want to limit the Disk Analysis Tool of CCleaner Professional Edition to a certain large directory. It only allows selection by hard drive. So I used the substitute command to isolate the directory to "drive X:" by typing in the following command:

SUBST X: "C:\Users\Gregorio\Desktop\!!!AnalyzeThisDirectory"

which is recognized at the command line and in File Explorer.

But it is not recognized in the Disk Analyzer menu.

How do I make this work?