Foreign Object on Decorator Crabs?

Just thought I'd ask the question, but has anyone ever put anything foreign onto a decorator crab? Something not of nature, to see if it might stick? I'm only asking this question because, SOMEHOW a beer bottle cap found it's way into my fish tank in a position which I can't get it out without causing mass destruction. What would occur should this decorator crab of mine stumble upon the beer bottle cap and turn it into a hat?



Anyway, the idea is cute, at least. For now my decorator crab currently has pineapple sponges all over him.