According to the rules, he can't:
- Mafia Pirate (Mafia) At a night of his choice the Mafia Pirate may choose a Townie he wants to steal the ability from. From that point in the game, the robbed Townie's role changes to 'Townie' without him knowing it and the Mafia Pirate is free to use it as his own. The Mafia Pirate knows the ability stolen and uses it at the proper Day or Night phase that the stolen role demands. All original clauses of the stolen ability apply. If the Mafia Pirate tries to steal the ability from a Mafia or a Third Party Member as primary role, the Mafia Pirate dies. The Mafia Pirate does not have the ability to kill at night like a normal Mafia member, only if the stolen ability allows that. (Game 41)
So if Van did target Gaj he should have stolen his role back then but we all know Van is way too careful to not waste MP on a random townie role.