Thanks for the reply.
Well, not much has happened, and not the greatest pics. Basically, I bought the cheapest piece of acrylic I could find, and glued it to the glass walls after drilling. Even if the silicone doesn't stick to the acrylic, sticking to the glass will keep the divider from moving, and it doesn't need to be incredibly strong with smaller mantis.
The drilling....first time, so made a few cracks. Basically, having a very fast drill and not letting it drop through the sheet is the key to drilling.
Some bad pics, lots of cleaning to do, but enjoy:
