When I want to exit a Primo with a flip trick, I make sure my back foot is past the rear truck on the edge of the board. This way, when I throw the move, the board gets a little rotation into it, making it easier to invoke the flip and also adds some shuvit flare.
Basically when I'm ready to throw the move, I pump my body down, then flip on the uprise, starting with my rear foot. It tosses the rear of the board into a loop and then I throw the front foot to make up for it on the other end. After that, try and make the board get stable under you and land the shizzle.