I wonder if this is posible. (if we ignore summonable ones)
Not counting scenario ones.
Few things that should be done:
A) you need to kill all bosses --) either on heroic or normal.
B) special heroic bosses must be killed (sinestra)
C) you can have help (you need it for some raids)
D) trash can be ignored (a premade raid cleans the trash and invites you into a raid and you just kill bosses and go out to next raid)
E) You cant split into groups and kill 3 bosses in same time. You need to stand at least 40 yards next too the boss and do some damage to him.
F) Everything must be recorded
G) You need to enter the raid over the entrance (you can be summoned outside)-- lfg dungeons dont count!
I am not sure for instance lock. (you entered too many dungeons)
But world bosses can be ignored .
I belive its posible if you have a good guild and have enogh friends to help you out. I can for example kill bosses in settek halls in less than 3 min (on a monk).