Without being aware of it, you have answered your own question.

The goal here is to build endurance, and whatever method you use to go about achieving it is a personal one. If you start a practice session with a certain fingering on a given scale, play it until it feels confortable as you go up and down the fingerboard. While keeping the page open, try another fingering on another string (same scale) and get used to playing that one as well.

You will then begin to notice that your ability to vary different stings crossings etc., shall expand as the sessions get longer. As a result you, and not the music, will be the one in total control of what you are doing with complete freedom. No scale etude can help build this level of athletic performance in such a way. Lastly, the use of a metronome is not essential for this kind of practicing. When following the bowings in order, they will automatically generate the necessary rhythm that is needed to create this endurance.

I hope that I have done my best to answer your question.