As far as I know, the specialist brokers (HiFX and CaxtonFX, for example), deal with money transfers rather than currency exchange. I suppose that you could try depositing money with one, and ask for it to be transferred to a sterling account of someone else (a spouse, for example!). Best to contact them and see what's available. If nothing else, they might give you other ideas if they can't do anything for you themselves.
If you literally have only a few dollars (like $10) there's not much point spending a lot of time on it - just let the bank rip you off and then forget it!