You can arrive at MCO and then head to the Mears counter. You can arrange for a ride on their bus/van to your WDW resort. And you could be put on the DME bus, but you will have paid for that ride.
That's the only way you can ride DME to your resort without having made a prior reservation.
Otherwise, you can book DME the day before you arrive in Orlando. But..you won't get your info packet or luggage tags...obviously. But, you will be in the system. I would just head to baggage claim and get the bags and bring them to the DME checkin area with you, then to the bus with you. You will be expected to tip the driver and bell services at the resort, but it's easier than giving the info to the DME people and having them retrieve the bags.