Many years ago when I first started teaching guitar lessons, my good friend, band mate and fellow guitar teacher, Mike, showed me a technique he was teaching his students, so that they could measure and regulate the control they have over their fingering on the fretboard.
He called it “The Crab Technique”. It was difficult, but it was helpful.
I decided to use that technique idea as a way of playing it as an alternative approach to the relatively boring, commonly used linear stretching exercise - only my idea was to alternate the fingers and strings as a way of developing muscle memory and a finger stretching exercise practiced outside of the linear box shape.
NOTE: Be sure to use your metronome for this exercise. I suggest starting out at a slow tempo (around 50-60bpm), then gradually increasing the speed as you get used to the exercise.
Also, remember that you are playing 1/8th notes; and that means using alternate picking!
I strongly suggest that you practice this stretching exercise every time you pick up your guitar to warm up. It is a great way to increase the movement in your fingers.