Why would you suppose OP can't change the flight? That's the very first thing I suggested.

It's entirely possible that OP can simply drop the last leg due to the lack of PE. "I'll find another way home from SFO." If that doesn't work, it's still possible to change to terminate at SFO; it simply may require a fare difference. (or, as someone suggested, OP may be able to add a stopover). If the price change is reasonable, OP may be able to get the employer to reimburse it in lieu of a flight back to SFO from EWR.

Sure, OP could also try to violate UA's CoC and use hidden-city ticketing, but why? I really don't see the upside here, at least not without exhausting other options first.