[xmonad] Putting PID into window title?

I sometimes spawn multiple instances of app that puts important information in the titlebar of its main window, but doesn't put the information in the titlebars of its child windows. When I run two instances of this app on the same desktop, it's difficult to tell which child windows are associated with which main window. If the PID associated with each window were in its titlebar, I could match the child windows and main windows up easily. I have checked that the app in question correctly sets the _NET_WM_PID property, but I don't see anything in Decoration or SimpleDecoration for letting me add my own text. Is there a way to do this? Thanks, -Joe G.