I don't know for sure but if the "quick drive down a bumpy road" method doesn't free it off then getting the back wheel out, the drum mechanism out, and re-setting the handbrake adjuster is probably the only reliable way of sorting it out. There is a port in the back plate that is probably designed to allow the mechanism to be re-set with the tip of a screwdriver but on the M3W you'll need to take the wheel out to get access to the port so...
If you do take the wheel out I would suggest that replacing the locator block between the shoes with the adjustable type is a smart move, it really does make working on the brakes much easier.
From the Alternative Parts List it is; "Replacement manual shoe adjuster, mod to fixed item. AP Lockheed v4158-129 SP, Delphi LA18129, Ford 1560018, GM 9961958"
