personally i would do ORD and request to be waitlisted for the direct BRU-IAD flight. i avoid LHR like the plague especially due to the departure tax on a J ticket.

i would also echo the other person who said look for something thru FRA, ZRH, MUC, etc...

regarding farelock I am not sure if you are elite or not, but if you are you will have reduced or non-existent award redeposit fees so that is almost as good, if not better, than farelock.