For the last couple of years I've been using the 2nd series Dwi pada entry (both legs behind head), now I had to try and remember how I used to get into it the old way. I used to do something I called the Supta K shuffle but it took me a week or so to re learn it. I'd always meant to film this as I've come across several bloggers mentioning that they struggle to get into the pose without a teacher to cross their feet for them.
So here it is while I remember, the trick is to shuffle the left foot as far over to the right as possible so it meets the right foot. Use the outside of the top half of the right foot to lever the heel up and over the left foot to hook them together, then you can move both feet to the center of the mat and curl your head in. You can get in tight enough that you can lift up almost as if you do have both legs all the way behind the head.
and here's the Supta K shuffle on it's own.