I frequently use Google's handy freeware CAD program called SketchUp. Although I haven't had any problems either with or created by the application, I wonder if it could conceivably be added to CCleaner's "Cleaner-Applications" list like Adobe Potoshop 7 and Adobe Reader? On the other hand, perhaps it doesn't accumulate "cleanable" garbage like some other applications. Being one who is at most computer semi-literate I simply don't know.
Check with the program's author & see if they have anything posted about temp files etc & how to manually remove. With this information you could add entries to CCleaner to remove them.