More than once I've watched people pay US$250 for WT > WT+ at the counter in the US.

Depending on which flight/day, there's a fair amount of W availability (some T but not every flight) ORD-LHR next week (thus speaketh EF) so I imagine the counter-pay scenario is certainly possible.

There's also a lot of J/D/I availability too, so who knows what joys the lounge lassies may be able to invoke.