I ended up taking my new/old fixie to a local bicycle frame welder who advertised his services on Craigslist. If he manages to bring my injured frame back to life, I'll sing his praises here - stay tune. After talking with him via email and showing him the photo of the damage, he thought the crack might be fix-able. For the quoted $30, I figured it was worth the risk. He can't destroy it any more than it's already destroyed.
I spoke with another semi-local frame builder/welder last week who didn't think it could be repaired. He also mentioned that he was backed up with work, and that his summer was going to be cut short by the arrival of his first kid. So I'm thinking he didn't want/couldn't spend time on a rinky-dink fix like this. At least, that's what I keep telling myself.
On Saturday, I stripped the paint off the damaged area with a wire-wheel on the grinder; the crack definitely seems to follow the joint between lug and tube. At no point does the top tube appear cracked. Fingers crossed. I figure once I get it back, I'll put some weight on the top tube itself and see if there is any indication of immediate danger/destruction.