He's not a master of evil, Frankenstein is a fanatic scientist but doen't have the evil intentions of Vampire Masters or Werewolves. He's also not dangerous enough as a gaming character and usually works from the back of the battle.
You could allow him the female victim rule and in that case he should have to use the Monster as guardian character. You should have only one female victim on the table though so if both warbands use it just roll a dice to see who get's with the girl. This would also fit into the Frankenstein background, he either tries to capture the girl ot to keep her.