I don't believe MM needed Locke's dead body to come back to the island to take it's form but rather to have a "Locke resurrected" story so he could continue his master plan. On the Island miracles of healing seem to happen and so when "Locke" is seen alive, all believe it was the islands doing. Even Richard, while a bit skeptical, seemed to buy it. MM set-up Locke the whole time, and had Locke's body not come back, his plan was dead. Nobody would believe that Locke just showed up on the island, they needed to have the body make the trip. "we know we brought him back, so seeing him alive, while weird, is possible on this island". Heck, we all bought it until the end.
I also believe that MM has control of all events on the island, up to the point that a human can make a decision to do something. He can't make them do anything but he certainly sets the stage to lead them the way he wants.
Prediction: The Donkey Wheel is a "prop" for all intents and purposes. MM controlled all the flashes etc. Having it "accidentally" come off it's stable point created the cause/effect us humans need to justify an event. "of course - the DW was off kilter so naturally time flashes". Suckers. In fact, all the unexplainable is created by MM....now if we just new who/what he really is.