I wouldn't lower the roof onto any supports to take the load off as this could result in one of the cables coming off the pulley and getting wedged, which would be a whole different disaster to deal with!
On the Coleman/Fleetwood whiffle-tree setups, each corner is drawn up individually. It would take a catastrophic failure of the whiffle tree or brake assembly for the roof system to let the roof drop, and even then, the door will hold it up. Trust me... It will not let you lower the roof with the door in place. (Everyone tries this once by accident at some point in their ownership!) In the event the brake refused to hold, you could always secure the handle to the bumper in a pinch. :)