A bit of clarity needed. LAS-JFK-EZE-JFK-SFO is only around 15K miles round-trip. How do you plan to make up the remaining miles? Which dates?
Also, look at ASU instead of EZE to save a few bucks. One of the routings is via EZE on the return, but for less money. I'm even seeing $1700 out of LAS, but not via JFK.