When I had to break down my 50 to reseal it, I had an established 29 that I could put the occupants in for a bit... Yes, they were crowded, but it was only for a few days while the sealant cured. I also didn't have very many fish in either tank, and could crowd them for a bit.
I just put the filter pads in the aquarium, in the back... I figured that would at least help keep the bacteria alive until the new tank was set-up. I wasn't dealing with potentially aggressive fish like cichlids, however.
I would get a rubbermaid type of tub for the fish and put it where you want it to be... don't try to move it full. I'm not sure about how to deal with filtration, though... you could put the filter media in the tub to help keep the bacteria alive, but I'm not sure what you'd do about aeration... bubblestones don't really do that much good, apparently.
The tank water doesn't do that much in the new tank, other than helping them adjust quickly... it would be the filter media I would be concerned with saving.