Topofthestack
This was indeed considered, we looked at giving all STN based a/c a different callsign, the proposal was 'jaffa' for the very reason you mention, however when it came to allocating another three letter identifier this posed a problem, nothing to do with the AOC. We probably could have asked ICAO for another three letter code, however, that in itself opens up a can of worms, and in the end was only dealing with part of the issue.
Your final suggest occurred to me to, why not get your SATCO to speak with our man in Luton?