You could always purchase a few extra, I believe there may still bea 40% bonus promo on at the moment (apologies if it already ended). I haven't got the tables to hand, but you need somewhere in the region of 20k per leg for East Coast USA, so if you had 40k you could do WTP and use UUA to an East Coast US city return. Remember there will an uplift in the cash element ex-LHR. Plus WTP tickets are not all that cheap at the moment. You could try starting in Inverness to avoid the Airport Departure Tax at LHR