Oh, that sounds cool. I'd like to know about that one, too.
I wonder if one can be made fairly easily? Make a shim shorter than the bottom board so that when it's fully inside the hive bottom it leaves a space along the front for the bee entrance, attach #8 hardware cloth to the top, then just put a sticky board underneath (trimmed to fit), and slide the whole thing in. Does that sound like what you're looking for? I'm trying to think of what would be good to use for the shim - thin enough to fit, but thick enough to keep the bee legs from going through the hardware cloth and touching the sticky board. Not coming up with anything at the moment, but bet I would if given enough time in Home Depot.