If you didn't have your holiday to think about, would work be paying for you to fly LHR-SFO-LHR on 17-21 March in WTP?
If so, that would currently cost over £3,000 to book (as there's no Saturday night stay involved)!!
Your best bet is probably therefore to get work to book you a LHR (or DUB)-NYC-SFO-LHR ON 13/17/21 March, which you can currently get in WTP for £1,600. You just them cancel or ditch your original ticket but still be on the same outbound flight to NYC as the rest of your friends.
Seems like a no brainier to me.