I do what sounds like the same stretch, but from a horizontal position - lie on your back, legs flat; raise one leg straight up in the air; either grab your big toe (if you're flexible) or loop a therapy band around your big toe; and gently pull your (straight) leg across your body. Like, for instance, if your left leg is in the air, pull it to the right. Hold for a while, then switch sides.

Hee, stretches are so hard to describe. They always sound ridiculous when you write it out like that.