Star supply is not hard to get. There are plenty of CEs, CCs, skills... The important thing is buffing his buster crits and Merlin is the best one at that.
If you don't want to use Merlin, Chiron's buffs are pretty good as well (IIRC, you do have him?), but you don't want him sucking up stars since Archers have the second best star weight, so it only works on fights you're able to 3-turn (or get close to it), and you'd need Combat Uniform to get him out of there.
Alternatively just use a really good Buster crit up CE (Victor of the Moon or Joint Recital would be best), level it if you can, and rely on just Hans for the additional crit buff.
That's not the ideal strategy but I doubt that's your objective. He should deal some good numbers anyway.