I've never heard of expediting mileage posting. Either they post or they don't. And the odds of getting upgraded on the return are very small.

But even if the miles from the outbound don't post before you fly the return, I'd think you'd get the 50% bonus for the return flights, because the miles from the outbound will almost certainly post before the miles from the return flights, and therefore the system should recognize your status when it posts the miles from the return.

Welcome to elite.