get icon manager to display a transient window

For some reason, the “spectacle” program produces a transient window. (This is a program for doing screen captures that I am running from the command line or from a FVWM2 menu.) It doesn’t vanish on its own, so it doesn’t really behave like a transient. And then if it gets buried it’s hard to find, and if it gets minimized it’s really hard to find.

How can I get the icon manager to include this window in its list?