Manipulating local GUI variables without using server scripts?

What I’d like to do is make a button that increases a local GUI variable by 1.
I know how to do this with NWscript and the SetLocalGUIVariable function, however I’d be interested on doing this all inside the xml.

What I’m looking for would be a function inside the xml that would essentially look like this:

OnLeftClick=UIObject_Misc_SetLocalVarString(local:1, local:1 + “1”)

Is such a thing possible?