You're in the wrong thread. :-)

The main benefit of most immediate mode guis I've seen is that it's trivial to expose internal values to a ui in one line of code. No callbacks, no looking for the right place in any XML file or similar. Instead you add these lines when you need them and they show up in a ui:

   checkbox(&godmode, "Activate Godmode")
   slider(&enemy_aggro, "Enemy aggression", 0, 100)