I am very fond of exercises with fixed fingers as seen in the last pages of Abel Carlevaro's Book 4. What I do is a little different, but probably came from Carlevaro or perhaps someone else. One finger per fret, I place a finger on the third string. The other three fingers play on the other strings. I also do the exercise with a fixed finger on the 6th string or 1st string.
I only do one of the exercises in a session; I don't do all of them in one session. I mark it in my practice log so that I mix it up and not neglect the exercises.
To me the point of the exercises is to make full use of shoulder, elbow, and wrist movement. As a last resort, fingers have to get involved. To me, it is more about maximum leverage from the shoulder, elbow, and wrist. And then learning coordination of finger movements rather than stretching.
Dr. Todd Tipton, classical guitarist
Cincinnati, OH, USA (available via Skype)