Apparently there is a method using sword block to return to the first side of the bridge. While on the far side of the bridge, you build the bridge, kill the Swordbearer to remove Crota's Grasp (which stops you from jumping back even with a sword), and then walk back over the bridge using a heavy sword's block to cancel the no sword debuff (forget it's name), rinse repeat. A random in a group I raided with not long ago was talking about it. Surely the video is out there. I know you can still beat the bridge alone using Warlock self res, but then you wouldn't get Flawless Raider, but you could still get Raiding Party solo. At least this much is true.