As you approach the berm you want to be crouched down with your feet reasonably parallel (due the position of the tyre with the ground at this angle there is less need to dig your foot down on the outside as in a conventional corner. Approach the corner in this position from the near to top of the berm. Not the very top (this is the berms weakest point). Near the top you will be in a position to gain maximum speed around and the berm and most importantly out of the berm as you exit
As you get into the corner bend into it and towards the ground. The G force keeps you on. There is a bit of faith required here. The combination of speed whilst having your centre of gravity down and into the corner keeps you on whilst building momentum. Again keep your knee facing into the corner out and down as much as possible.
As you leave the berm come down from the top of the berm to the middle and rise slightly and straighten up and reposition into the bike and start pedalling to keep the momentum flowing and prepare yourself to crouch if required to enter the next switchback and repeat with the positions swapped round.