In my group we use a simple drill. I have no English term for this exercise, but it is quite simple:
First position yourself on your shins on the floor, hips extended, upper body erect - like the letter "L" if you know what I mean...
A training partner should fixate your ancles, giving your legs a anchor point.
Now this drill can be performed in several ways. Usually we introduce it in this form:
Fall forward to a prone position. Once you are prone, you push with your arms without any significant bending of your hips, then pull with your hamstrings in order to return to the initial position.
After a period of training with this drill, we slowly reduce the contribution of arm impulse, thus making the hamstrings work harder.
Then we switch to eccentric work. Instead of falling to the prone position, you try to hold back the forward movement with your hamstrings - think "fall as slow as you can" - again without any significant bending of your hips. Once prone you push with your arms to return to the initial position.
Usually we do the eccentric work for 6 weeks - starting some 10 weeks prior to an important meet.
Come to think of it, dead lifting with stretched legs are also quite useful for hamstring development. You could also try walking with small steps (1 foot) with your hips flexed in order to touch your toes for each step. The upper body "rocks" up and down for each step - basic work for the hamstrings.