You may have to cut off the lock by cutting into two or more pieces using a hand held cutoff saw/grinder. Abrasive cutting wheel on these tools can cut through concrete, tile, steel... It's not clean but I'm sure it can cut through pinhead locks.

You can also try LBS and they may be able to get it off without destroying the lock. I'm just too impatient. If you decide on DIY with a cut off saw using an abrasive wheel, make sure the seat post, the bike frame do not get too hot. You may have to pour cold water every so often while you try to cut through the lock. Or take time to let the parts cool off.