Unusual exercises for improving hamstring flexibility

Here's an article from Z-Health recommending exercises for the back of the neck - to improve hamstring flexibility.  Worth a look I think...

http://zhealtheducation.com/episode-108-improve-hamstring-flexibility/

Another hamstring flexibility routine, this time from Functional Patterns:
http://www.functionalpatterns.com/tight-hamstrings-stretching-routine-for-posterior-chain/