Could you add a method to swap IUP and RmlUi in the rendering and input z-order?

I've been experimenting with RmlUi and various ways to possibly enhance the UI, but one road block that I've encountered is that IUP appears to be blocking inputs to RmlUi interfaces.

For instance, I've been mocking up a new chat window which can display a context menu for common player interactions, if you click on a character name. I've also long thought tabbed channels had some merit, so I figured I'd play with those. Unfortunately, IUP is blocking clicks to the RmlUi elements.