I've never heard of someone who could only move the fingertip, maybe with a nerve damage from injury.
I want this animated so we can get the bdsm fanart, because I don't think this isn't as huge as WataMote manga yet where each chapter is an excuse to make more.
If you're having trouble stretching your fingers to reach different frets, take a look at this video. It's some tried and true advice from a trusted individual...