Just on this past Saturday, when using the First Class check-in at JFK, the desk agent recognized there were 3 of us (me, wife and teenage child) and only one EXP. So she volunteered to call up to the SoHo lounge to add an access pass. When we got up to SoHo, the check-in agent immediately said only one guest is allowed (by the book) but when we mentioned the call-up, she said yes indeed she got it and we are all welcome in. Now I believe FC desk agent took pity on us for being caught up in Heathrow fire debacle, but the possibility is there. YMMV