Here's an Idea for a set-up...
Esay access to the Sponge and Carbon bag.
The drilling the plate could take some time, but would be well worth the effort.
Something like few holes close to the water inlet side, to more holes the further away. (better to start out with very few holes and test. Then adjust with more holes, than patch up holes)
You could put some braces here and there to hold it up off the media.
Egg-crate(light difusser in hardware store)
Would need some braces one way or another.
Anything from tabs on the plexi-glass on either side. Peices of pvc tube stuck to the bottom. etc.