[Falkor]

I would try the following:

Two small squads (2 x 10 Militia) in the right corner scripted: attack rear and hold + attack rear.
Guarded mage placed in the opposite right corner a bit to the back side scripted: attack one turn, 4x Charm, retreat.

This should give the mage time to cast the spell undisturbed. Retreat after 5 turns saves the mage. AI will probably choose evererything but not charm for him to cast.

Advantages:
-Repeating until successful.
-Get rid of some unwanted upkeep suckers.