My Slur eBook did not include exercises dealing with slurs using the first finger. Big thanks to Perf for pointing this out. Ascending and descending slurs from and two open strings come up very frequently in repertoire.
A Few Exercises
First Finger Slurs (PDF)
All of these are done on the first string. Just like the other slur studies are moved to different strings while retaining the same intervals and fingerings, these exercises can (and should) also be moved to any string.
Some music includes slurs to and from open strings with other fingers: the fingering can be altered to include other fingers, as well.
Any of the rhythmic variations or slow/fast alternation explained in the eBook can be applied these slurs as well.
Angled vs. Parallel Left Hand Positions
Guitarist spend time in both angled and parallel left hand positions. Slurs should sound good using either. It would be wise to practice these exercises (and the others, to some extent) with both angled and parallel hand positions.