All they would have to do is announce that they are changing parties and start caucusing with the Democrats. Zell Miller caucused with the Republicans, while continuing to claim to be a Democrat. Jim Jeffords caucuses with the Democrats, while calling himself an Independent. Party labels are whatever the Senators make of them. Mark Dayton, from Minnesota, was elected in MN as a DFLer (which is the state affiliate of the Dems), but he's just a D in the Senate.

As for how it would happen, they'd likely be wooed by Reid, who managed to convince Jeffords to switch.

As to whether it would happen, that's unlikely. Think about getting pork for your home state and think about trying to do it after gaining the ire of the party that controls all of Washington.

Maybe if we had won. There's no way now that we've lost big.