Well, this is embarassing.

[DebW]

Where's DebW when we need her?

The center wire that connects the two arms has one end (on mine, the left) that is firmly attached, and the other end (right) has a round barrel-shaped stopper on the end. When I squeeze the arms toward each other, and get some slack in the center wire, I can pull the barrel-stopper out of the right arm.

My apologies for not being here (but I do need to sleep). KnottedYet is exactly right. But Snap, if you're ever stuck and can't get the brake open, you can always let air out of the tire until it fits through the brake.