I know it's perfectly possible to bypass the quest and continue the main story by various means, but could you complete this quest by killing all the ghouls? Seems like that would solve Manny's problem, and I want the XP for killing them/completing the quest.

But it is so much more satisfying to complete the quest!

Besides, I think you'll actually earn more XP by completing the quest. You earn 800 XP for the quest, I think, plus additional XP for convincing the human guy that he is, in fact, human, for correcting the rockets' trajectory, for side quests for Harland and for the Nightkin fellow, etc. I don't think you can get that much XP from killing them.

It fits my character better, and it was a boring quest: I've done it once before.

I've never done it that way, but since Manny/the quest says "by any means necessary" I'd be pretty surprised if killing them all wasn't an option.

I've killed all the ghouls and completed the quest with a mellee,unarmed character on my last play through.
If it fits the character better do it.
The only thing is that you don't get the quest completion award.

You could do that but its better to finish the quest as you get more exp.

If you want to kill them, just reprogram the rockets to crash into each other. Killing them any other way should give you a quest failure.

You could bypass it completely by going into Manny's hotel room and reading what's on his terminal. This gives you the info you need to continue the main quest, and you can always come back to "come fly with me" another time.