I think I would do the sponge, like Pitluvs said, individual filters would be a lot of plugs.
However, I don't agree with needing tempered glass. Normally I would say yes, at 1/4" thick it would have to be tempered, but... If he built a custom tank that was only say 8" or 10" deep and had a glass wall siliconed in every 6"... there would be enough strenght in the deviders grip and not enough presure with only 10" deep to need tempered. Each of those walls would add strenght.