Here's a progression for release - from double extension release through to a single leg flexing release (inside leg). The latter much in line with
@LiquidFeet post. Drawing your attention to a couple of points:
1. Anticipation of the upper body to the inside of the new turn mentioned at 0:35. (If the torso is already on the way out of the old turn - or about to move out - then the effort/movement involved in initiating a transition is very small. Of course can be a big movement for more rapid effect.)
2. Development of the platform on the new outside ski mentioned at 2:25. (Doing drills such as up and over, high five, downhill skating are all great for this. So are slippy grippy turns.)
3. All skiing is much easier with a flash new ski suit.
Also worth watching the same guy's earlier vid wrt point 1 above. (Alas, old ski suit...)
All these transitions involve hips rising into transition. To progress on to double flex to release - keeping hips low - a possible path is through retraction/extension turns. If able to do a passable version of these then should have the balance skills to do them in carving situations. (Note: two flash ski suits are even better.)
Be interested to find out how others have progressed from high hip transitions into double flex to release.