Unless they have changed something since I last looked at UI stuff here, this is not possible.
The UI isn't scripted at all, just XML docs to define the pulling and display of graphics for the most part.
Some areas you can pull some little tricks, like the healer helpers that target the party member before casting a spell, but that is about as complex as you can get.
Not to discourage, it will be great having another person willing to author UIs and components