It's 100% allowed. But Disney won't pick up your luggage. You have to get it yourself and take it to the ME bus.
If you call up, get a cast member who understands the rules and knows how to put you in the system without a flight, you'll be fine.
However, many folks find that it's a whole lot easier to just tell Disney you are arriving on a flight for about the time you want to be picked up. It seems to make them happy.