Just a quick addition, I have a tip for you to not only train that finger a bit, but get a bit of exposure, someone once told me this and it worked.
I wasn't looking to play with three fingers all the time, but just sometimes throw the ring finger in there to make some riffs a little easier. Anyway, I used to use just two fingers, thumb on the pickup and my ring and pinky curled in a sort of half fist, no pressure, but out of the way.
Anyhoo, I was told just to use two fingers but keep all FOUR straight and over the strings, before long i noticed that riffs where becoming easier for me, especially paster ones that involved triplets. I had no idea why, whenever i concentrated on my right hand, it would become harder.
During band one day, my drummer said after a near perfect rendition of Whiplash, that my fingers where going nuts, I asked him what i was doing, and he said that I was playing with three fingers. Not consistently but especially during the solo riff and occasionally during the verses. I was very proud. Like I said, I dont realluy play with three, but i occasionally (and subconciously) throw an extra finger in, it helped me alot.
But remember, Each to their own. It worked for me, I hope it helps you too!