Sounds fun! My only advice would be to use glass or plexi for the divider, silicone that in and then attach something like wood or some slate to it for a more natural appearance. I have tried more flexible plastics in the past with poor results (might have just been me though) and think it would be much easier to hide a piece of glass than to actually use something aesthetically pleasing. Having the glass be at something other than a 90 degree angle also seems to do wonders for the appearance of a vivarium.
Well, good luck, and do post how it goes.

with envy,
duncan