I've always played those first two notes with my ring finger, as I tend to keep 4-finger positioning all the way down the neck, and I guess what I do for the articulation would be considered a "ring finger roll." I just tried the "pinky and ring" fingering after reading this post, and it works well too. But I've been doing it with the ring for years, and I think just easier that way, pinky or ring and rolling. As long as you play the first note long and the second short, which is how I've always heard it.