I'm not talking about representations of gods. Now if you want to say that you're a god tongue in cheek, that's fine with me, but on a very basic Japanese level, I'm just saying that 外神 seems to me to literally refer to gods, not people.

Any metaphors you like to make notwithstanding, I think very few Japanese people would ever make the connection to "divine foreigner".
It clearly refers to gods, no Japanese is going to associate Shinto deificiation with a foreigner's afterlife, at least in the absense of any other context, and everyone knows that everyone else knows it. I vote we not make that into a humourous t-shirt.