it is already in the code. It looks like some creature action is required to redraw this. I tried virtual actions as BM:V (showing a spell animation) but no effect. It needs BG action.

I recall Sav wrote a piece of UN:C code allowing the redraw a creature movement range in battle (if you change speed for example). I think that would work, but can't find it.

@Edit: found it

No effect on bf redraw

Tested a bit more: battlefield will redraw if:
a) open magic book and select a spell (don't need to cast)
b) open combat options (only have to open it)
c) of course, move the creature