The edge crease tool is very limited and will not give a good result in every situation. In my experience situations such as the one you're showing have to be dealt with good old retopology techniques.
Adding loops doesn't have to mess with the curve of the cylinder. Here is a suggestion on how you could deal with that crease without messing with the roundness of the cylinder and still having only quads (although I used two diamond-like faces, they're still quads - except for the big N-gon in the bottom of the hole that was already there, I mean):
This is just one possibility that you can try out and see if the result is good enough. But you can come up with other, perhaps better, solutions on your own if you do some trial and error.