AS far as I know:
AEO - do the SEMC course at HMS Sultan, Gosport. During this time there will be a call for volunteers for Test Pilot/Obs. Those that volunteer then go off to do aptitude tests. After Sultan you go off to Yeovilton/Culdrose/Wittering to complete your Engineering Certificate of Competence on the aircraft type you have been sent to (although the CofC is valid across platforms, a friend did the Sea Harrier CofC before going onto a rotary Squadron). After successful completion of your CofC you then go off to flying/observer training. On completion you do an operational tour on a Frontline Squadron before doing more test pilot type stuff and becoming fully spammed up.
The fact that you have already done aptitudes, missed out on pilot and got chopped on BOC may prevent you from going down this route but you never know.
Personally I have thoroughly enjoyed my time as an AEO so far, but if you are going to be bitter about the fact that you are working with aircraft not flying them then you are better off going down a civi airline path.
Hope this helps,
