dude, i had the same problem when playing faster lead stuff on acoustic. it takes a little getting used to; i anchor my pinkie on my middle pickup on my strat, its so comfy for me, and theres no pickup to anchor on when i play acoustic. the past 4 months or so ive gotten incredibly better at playing lead on acoustic, and i actually prefer it for some stuff. once you get used to switching string guages (from electric to acoustic) you can get used to playing fast on it, and worry less about anchoring your pinkie. i can play a bit of gwinge malmsteem **** on acoustic to warm me up. after playing lead on acoustic strings, it seems a hell of alot easier on electric.