Hmm.. you would have to add it by Package instead. addPackage()
But in the current ShrinkWrap version it relays on there being a Package, and a Package only exists in the ClassLoader if a Class in that package has been loaded. Since this is a lonely class that is not refered to from any where it probably won't be. Next version of ShrinkWrap supports loading Classes from packages without going through the ClassLoader, which should help in thee cases.
Maybe this hackish workaround would work for now?