Haha, this is getting interesting. When you take everything into account, it breaks even almost exactly!
I'm going to try to book LAX-LHR-EBB...EZE-DFW-SFO.
If that doesn't work, I'll try ORD-LHR-EBB...EZE-DFW-SFO.
As for mileage optimization, that really isn't the goal at this point... but I might as well ask

I suppose EZE-JFK-SFO would give me more miles. Any other suggestions?
-Nick