After alot of experiementing and tries and timing we finally got it. Too bad I didnt think of this earlier :P
Ill try and explain as good as I can.
First of all the setup we had was
1 warlock ilvl501 with engineering (important!)
1 prot pally ilvl~480
1 ret pally ilvl ~475
1 blood dk ilvl ~475
(Might be possible to 2man it aswell if you have a really pimped blood dk)
Now for the tactic. Warlock places his portal (using portal exploit to get past walls) at the side of the doorway into yoggs room as you enter it (See pic)
Now thats sorted you can begin the fight so let everyone run into the room and start killing the adds ontop of sara while the warlock uses teleport and then swiftly uses "goblin glider" from engineering and flies to the center where sara/yogg is (its in the center of the minimap if you use that as a guidance). After a little while you should be in yoggs brain room and you can start nuking his brain in advance. Now you dont wanna go crazy because if you nuke the brain down to 30% before sara is gone then its game over. So Nuke the brain down to like around 40% and then slowly take it down without dots so you get it to 32 or 31%. When thats done you just have to wait for the others upstairs to get sara nuked down (with the help of the adds). As soon as sara is gone and yogg has spawned which you can see on emote or someone yelling in TS/Vent/Mumble then you soulburn soulswap and malefic grasp the brain as long as you can til you cant dps more and then the shield is gone uptop and its phase 3 already.
Now there is a slight problem. You are stuck below and cant use the portals but I found out after a couple of tries that if the tanks and melees goes and hugs the door in the beginning (where you enter the room) then the next spawning add is likely to aggro you and you will get teleported up automaticly. This can also happen in the first phase just fyi and then you just have to have the melees killing the adds out of saras reach til your goblin glider is off cd so you can teleport and fly back down (didnt happen often but it did a couple of times)
If you reached this far then congrats, its almost done. The tanks and melee needs to take care of the adds fulltime while you nuke yogg as much as possible before they get overrun. Having 1 extra range or 2 even makes it easier ofcourse but having as few as possible makes it fewer people to roll for the mount
I did this as affliction with flask and food buff and just popped all cds, pot, soulburn soulswap malefic til boss got to 20 then just drain soul with the dots up which made it faster and easier since i got new shards. You will get stunned and sometimes spellocked for 4sec and all kinds of debuffs but just keep going and make sure that people dont get mcd by having everyone facing away from the boss, thus they will never get mcd in that last phase.
With the above tactic you are skipping the whole phase 2 in which you loose sanity really quick due to being so few ppl to spread psycosis (which luckily isnt happening at all in last phase) out on and all the other shit going on.
Also some of the adds that are spawning in that last phase cant be killed so you must lower their hp so that the tank doesnt get overrun too quickly as they do more dmg if theyre on full hp.
Also when you begin the fight, do not run ahead first as a warlock as you are more likely to get initial aggro from the adds and you will then get ported up from brain room asap.
Think i´ve got it all else just ask and ill answer the best I can
Edit: Also another tip just incase you overlook it is that you can start ulduar in 10player mode and basicly solo everything (except for thorim which can be tricky to time) and then just go out and set to 25man and walk back in to face yoggie
If you have trouble getting the portal exploit to work then you could use the mount exploit in freyas room to get through the wall, just check that russian movie below this post and youll see how to do it.