Automatic MIDI Assignment for selected control?

[Explodicide]

Is there a way to have Ableton automatically assign a certain MIDI controler signal to the selected control? Like, I've got an encoder knob on my Oxygen that's not actively bound to any specific input in Ableton, and whatever control knob I click in the mixer or on an instrument gets controlled by that knob until I select something else. Is that possible? It would make work a LOT faster for me.

Or, is there any hardware that can do that? I've seen some dedicated knob hardware that's supposed to be like a 'universal MIDI control'.

Thx