I think I see what he's proposing. Basically, it's a rappel. Divide the rope into two equal coils, one on either side of the beam. You can then slide down the rope. The other will come up and over the beam. Unfortunately, the beam will need to be propped off the ground, which may not be easy to secure.
Another approach would be to drive a couple iron spikes into the floor such that they are at a 45 degree angle. You can then thread the rope around them and it should be easy to pull one end once everyone's down and have the rope and be down on the first floor.