This is close, but not really Pascal's Wager. For one, I do not currently practice any religion. But if I did, I'd have to pick one exclusively, to the detriment of the others. So of course his wager is a weak argument.
But with posthumous baptism, it is someone else doing the thing. And multiple different religions can all claim me as their own. There can be overlap, maybe. (Or maybe not, who knows? We're in angels on the head of a pin territory here)
So, if the Mormons baptizing me causes me eternal harm, then both of the following would be true:
1. They do have supernatural powers after all. (i.e. Mormon rituals have an effect on souls, deities, etc.)
2. But their belief system is wrong.
I guess one can construct a system where both #1 and #2 hold, but I don't see it as being nearly as likely as either one in isolation.