I have a 3-gallon, clear sided, "Animal Cracker" bucket from Sam's Club, for catching spent primers from the Lee Press clear plastic tube. Pretty sophisticated, huh!
I too have been thinking about the phenomenon of primers ejecting onto the reloading table and floor. About 40% of primers eject this way. When depriming thousands of primers, this is a big PITA. I have yet to devise a way to prevent premature ejection of spent primers (sometimes unspent primers) from the press, and I have thought about it, but not experimented with it, a lot.
Perhaps a slightly tapered, slot-shaped and one-end cylindrically sanded, piece of wood that is hammer-fitted into that slot would be effective. How many handle pulls would it take before the slant-slotted-slot-seated-slit-stuffer ejected itself is an unknown. Seems worthy of a try though.