I'm not quite sure how to get pictures on here yet, but if you go to WikiMapia and find Space Mountain at the MK, follow the Monorail beam (dashed line on the map) North to the "Monorail and Train Roundhouse" (its really square...) and its the building immediately North of there, labeled "Walt Disney World Holiday Services." Sorry I couldn't figure out the picture, but Wikimapia is fun because it lits literally every building on property.
This site does not condone this sort of activity. And I suspect that once enough people discover this loophole, it will be closed, making things a bit more inconvenient for those who have a legitimate reason to be using these roads.