Also in the video I enter kurmasana via Dwi pada sirsasana (both legs behind head) this is an advanced entry to the posture that allows you to get deeper into the pose.
Before attempting the Dwi pada entry be sure that your comfortable with eka pada sirsasana (one leg behind head) from the Asymmetric and Supine sequences as well as perhaps Yoga nidra from the Supine sequence.
In the video I also raise my heels off the mat this too is an advanced version of Kurmasana. To be able to raise the heels the legs need to be high up above the elbow. Push the backside back engage the bandhas and stretch the legs which should cause them to straighten and the heels to lift. this gives an intense stretch to the hamstrings so they need to be nicely warmed up before hand with for example a long five minute Paschimottanasana or uttanasana.
It is sufficient to enter the posture from the mat, keep the heels down and focus on the breath as in paschimottanasana, short inhalations and long slow exhalations.
To get the legs over the head in akuncha kurmasana (pic 3) from the mat one 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. here's a link to a post and video from my blog.
Here's the video of the shuffle.