Things I've 1 tanked so far:
MV:
Feng
Spirit kings
HoF:
Vizier
Blade Lord
Garalon
Windlord
ToeS:
Protectors
Tsulong
With a lot of the bosses, we used a frost DK to take w/e debuff prevented the fight from being 1 tanked. I.e. on Tsulong we had our Frost DK take the third beath, which allowed my stack of 2 to drop, and then get back up to 2 before the next day phase. Same thing on Bladelord. Using a good frost DK and some healer cooldowns I think it would be possible to do elegon (use frost DK to drop stacks on current tank and to tank add for the 10 seconds its alive) and possibly empress (they would just taunt to get the eye debuff). We haven't tried ambershaper with 1 tank, but depending on the mechanics it could work. I think he would reshape life the frost DK second during P1, and if you can handle a hit or two during Fling in P2 you should be fine.
It really just all depends on your healers, because obviously we weren't 1 tanking these fights during any kind of progression, rather just to speed up our farming. If you are having problems beating enrage because of DPS then it doesn't seem like your group could handle 1 tanking some of these fights.