That's a good idea. You could use magnets to hold it tight against the keezer.
I have a smaller version of that. I made an oak box and inset a drip tray into the box. Mine is held on with small brackets and rare earth magnets, but a taller version could house the tray as well as a reservoir for the overflow. Hmm...Might have to take a shot at this.
Never underestimate the potential of someone who refuses to act their age.