Hi Marjerah, my tactic is to create a kind of "Wardian case" topper of a light weight plexiglass. As you know from another site I am creating a 75 gallon plaudarium now, and I am going through the same growing pains. You know, you think then figure it will or wont work, etc. Since I am incorporating orchids, and want to fill about 50 gallons of water I have dumped the waterfall concept and gone with "tree roots" as in a swamp with the tangled roots. This will give me lots of trickle areas. I also am going with a underwater pond pump inside a bucket or case which I will incorporate into the roots which will be my filter. (I will make the rock of fiberglass). One really great filter concept was to build a wall separator which would shrink your tank some, and use that as the filter. Built into the tank. That is also an option, and it could have a sponge draw.
By the way, looking for plants local to macrostoma, I found an orchid that grows in Baruni, Oberonia rosea. It is probably as indangered in its native habitat as our friend the macrostoma.