Gaining flexibility for the L pull up

Right now I'm not able to do full ROM L pull ups as I dont have the shoulder flexibility to start from the bottom. What stretches should I do to gain that shoulder flexibility?

Hanging, skin the cats, wallslides, cuban presses, pass-thrus/stick dislocates and perhaps cat stretch and shoulder extension and maybe even stretching your pecs like the bow of a ship.

http://www.massagebris.com.au/images/passion4health/articles/pec-stretch.png

I was taught to do this stretch with straight arms. My chest would be in front of my hands so it looks like the bow of a ship.

I've never heard of this problem. Can you do regular pull ups with full ROM? I personally don't see the difference.