In that case, what is the best way to do this? If I make big levels, full dynamic lightning is too slow.
Well if you need full dynamic lighting then you should avoid lightmaps at this moment and go to hardware lighting. If you can't do that for some reason then I'm afraid that for now you're out of luck. In the future CS will have better support for using lightmaps and hardware dynamic lighting at the same time but this is not for short-term.