The tugboat idea is good.
Sexp for a beam that has 0 damage a long life, no buildup/cooldown, and really really small fire wait 0.05 or so. And NO impact explosion. The ship would need to have it's beams disabled, or only selectivly enabled.
Sexp the turrets to fire at the same weapon turret or subsystem for continuity's sake.
The hauled ship should have a engine subsystem strength of 2% or so with sexps to keep it repaired at 2%.
Then waypoints and capship speed limits.
Definitely make sure the tugboat can't accept any player orders to attack or capture anything or else it'd run off of the waypoint and the towed ship would keep going.
And I don't think the negative damage modifier would work guys. I've read

of posts at the VBB of people trying it but failing.
Though I'm not going to stop anyne from trying it themselves, Nobody's perfect.