Just like in athletics I know it's important to warm a muscle up for stretching, but I feel like an -extensive- stretching routine for your hands...I'm not convinced it's really that necessary, especially for people who have limited time to practice.
I watched a stretching routine with John Petrucci. The guy was doing tricep stretches and massaging his pectorals. At that point you might as well hop on a flat bench press and start busting out reps.
I took lessons briefly from a professional musician and he doesn't bother with stretching in this way, more in the fashion of stretch warm-ups while playing the guitar and not pulling fingers.
I've settled on the in-between. I transcribe for television so that has me typing 8 hours a day. I come home and play guitar for the rest so I'm REALLY interested in keeping my hands healthy. I do some brief, gentle pulling and that's it.
You'll warm up with guitar exercises but you should stretch to prevent Carpal Tunnel. Here is a real simple way of doing it - first link in Google search - and it's doctor research. Hope this helps!
Carpal Tunnel Syndrome Exercises