The setup I'm thinking of is this. I don't know if it would work with ghasts but it sounds workable:
Machines and items involved:
(1) One mob magnet thingy from Thaumic Tinkerer (forgot the name)
(2) One Autonomous activator (TE)
(3) One bedrock sword (RotaryCraft)
(4) One mob spawner (MFR)
(5) A vacuum hopper (Extrac Utilities)
The concept is: spawn the ghast with the spawner, let the mob magnet draw it towards itself, which is right across the autonomous activator. With the bedrock sword (inifinite durability) in the autonomous activator the ghast should be killed swiftly. Collect ghastly stuff and xp with a vacuum hopper.
I have this working with a Blizz spawner. Shouldn't be too difficult to adapt it to ghasts.