I've been looking at his design for the o.h. for some time now. I'm planning to build one soon. I'm really interested in this:
Super Em Up

It is easy to add a 'super' or two to this observation hive. Such a super could incorporate an excluder and simplify colony management. Excess honey or bees could easily be removed without disturbing or removing the entire hive.
How exactly would one super this observation hive? Build another identical to his plans and put it one top allowing the bees travel through the hole on top? Edited to ask if the hole would even be large enough for that.
I tried to contact D.Murrel himself but he does not allow PM unfortunately.
Many thanks!