If the bike absolutely has to go into a bag to get past security, the Swift is sadly probably out of the running; that's too bad, as it's probably the most "roadie" possibility, along with some Bike Fridays.
It can get a lot smaller very fast, but is still pretty bulky & unlikely to get past the average NYC lobby guard.
I have to go up to my office in the freight elevator with my Swift, but wouldn't give up the ride for any front-lobby entrance/exit rights in the world.
If you've got to go through the front way, New Yorker is probably right that the Brompton is your best/maybe only bet. I would definitely buy one as a second bike if I could convince my wife to let me have more than one bike again (ie, probably next year).