Well, I have been in a same situation before and missed out b'coz i could not get an NOC. The Qatar Labour Laws are not much helpful on that, its up to your current sponsor to release you or not. There is one way though. Q-Companies like QP, QG, etc can approach immigration stating that you are absolutely necessary for their business needs. Then something can happen. But again it all depends on how far your new company would go to get you on board. The best way is to somehow make ur current employer agree release you. I know it feels bad, but you can't help it. Thats the way it is