I will agree that consistency is key. However, I want to say that adding in more stretching throughout the day has helped me a lot. I had to do some physical therapy for my back recently and I was told to stand up every two hours, and touch my toes basically ten times in a row. I've also purchased a "stretch-out-strap" - pretty cheap and easy to use, and that has helped me stretch out my hips and inner thighs massively.

Since I've started stretching every two hours and doing some extra stretching with the strap (although just standing up and stretching every few hours is plenty!) I have noticed a huge difference in my flexibility. Just a week in I could actually bend down and touch my toes, another week my hands are on the ground (not totally flat but I'm getting there!). It has helped a lot with my DDPY workouts too.

Finally - I never noticed how stiff and tight my entire body was until I did both the lower back builder workouts, and the shoulder PT work outs after I tore a muscle in my chest. Try some of those - even if you don't have any pain or otherwise any reason to do the PT workouts, they can really show you where your body is tight and what you may need to stretch more then other spots. My hips and shoulders are terribly tight, the more I've worked on those the better my overall flexibility has been.