Man I wish you had pictures. I imagine the line is the wastegate sensing line. when the manifold is under boost pressure, the wastegate opens by adding boost to one side of the bellows, which pushes against the mechanical spring pressure opening the wastegate, allowing exhaust to bypass the turbine. This is an educated guess, as you said the line went from the manifold to the turbo. Mine is a little different.

As far as options... you are about out of them. I would drill and "tap", although, I have had very good luck just kissing the female thread peaks with just the right size drill bit, and using a scribe, hook the brass threads and get them out of there. This eliminates you tapping the threads in the wrong place as compared to the originals. You will want to run a tap once all the brass is out of there as a thread chaser though.

I think you have no choice but to remove the manifold.

There is always the drill it completely out option (all existing threads), where you insert a heila-coil. Be sure you have the right material composition of heila-coil for aluminum. I think it is anodised blue, but don't quote me.

If there is anything left to get a hold of, you can try an 4" or 6" pipe wrench to get it lose. Brass is so soft though, might just end up breaking it closer to the manifold that way.

You sound like you know what you are doing, as you mentioned easy out, so I won't insult your inteligence by telling you which way to turn it. (Don't laugh... I've seen it all).

Good luck!