One hopes that with the acquisition of BD, BA and BAA are seriously reconsidering which terminals they will be using. If the fuel farm were re-located, and a further satellite (T5D) were constructed, could BA fit all it's newly enlarged operations within the one terminal?
Before veering off-topic completely, if the OP fancies stretching his or her legs, the people mover is complimented by this pedestrian tunnel between the satellite terminals:
Tunnel between T5C and T5B by
businesstraveller, on Flickr