I got lucky on my last attempt.
I put down a nest of mines and demo charges before Elijah came down. I glitched through the force field as he entered (no Stealth Boy but high sneak + magazine); he saw me but it didn't matter as I made it to the force field in time. I chuckled as he hit the mines but he survived with one pip of health left. Then he healed.
I was just about to reload when I remembered the 3rd person glitch -- I managed to get some c4 through the force field and let him see me. He walked right up to the door and blammo! that was it for Elijah.
Casual walk out to the elevator. Sweet.