Thanks for the tips, folks. We're fairly regular travellers to IAD ... the difficulty is the way JER sectors keep changing. How long will BMI keep the LHR option going, for a start!
Yes, we're going BMI to LHR outbound in late May. However, return is BA to LHR and then BA LGW-JER. Three weeks' clothing and some shopping tends to cross the baggage limits, and at least that way we get the trans-Atlantic baggage allowance on the x-Channel sector.
I'll take a look at some of those other options, although we were hoping to avoid either internal airline changes in USA, or a lengthy drive after a day or so travelling. At least IAD is just 45 minutes from where I'm headed, even with beltway traffic!!