These exercises, although labelled for splits, are amazing at opening the hips, hamstrings, and hip flexors:
http://katlaydee.tumblr.com/post/36863454708/make-sure-you-stretch-both-sides-i-like-to-do
Also, if you do any kind of yoga, the (screaming) pigeon pose can work wonders, as well as any kind of standing body twists.
It can be done, just takes time and patience!