UI_Dialogue was intended to be inherited instead of duplicated entirely (mentioned briefly in the documentation), I don’t think it would be straightforward to replace it with a new class entirely.
Another problem you will encounter is that the text and response widgets are “hardcoded” in the base UI_Dialogue file (this has been changed for the next version).
I’m afraid I won’t be much help beyond this though; the implementation that I can figure is far too cumbersome to describe
