It took me a minute to figure that out, but… excellent idea!
Let me get this straight. The snare is pre configured with an extra lock, a "slider lock" on the cable. Except this "slider" lock doesn't have any thing fastened on the leading end of it. When you make the set, you use a typically slide wire system, and attach the snare swivel to the slide wire. You attach the weight to the slider lock, and move this lock back towards the swivel end of the snare. You then position and stabilize the snare.
When the beaver is caught, it starts wrestling around in the snare. When the beaver stretches the snare cable tight, the weight starts working its way down the snare cable, towards the beaver, and the lock keeps it from back up, away from the beaver.
Buy the time the beaver works the snare down the slide wire, into deep water, it is wearing a brake rotor for a necklace.
-- Hal