The gc100-6 that I have does not have the relay outputs, but I might get a gc100-12 eventually, just to be able to controll the buzzer on the door in the hallway downstairs, I don't have a garage.
I think the gc100-12 could easily pull it off, it has relay outputs to control the open/close switch(es). And also ports that can be used for sensor input, so you could hook up the gararge door contacts to get the state of the door, I think (for now I'm still trying to figure out how these sensors work in LMCE).
Another option might be using X10 or similar, I have seen control switches for motorized sunblinds, that's basicly the same thing as a garage door I reckon.