You really don't need to pop high to do a vulcan, because the most important thing is that you stick in your nose as fast as possible. Jump around the first 30-90° and at the same time point the nose down into the water. I never do it over a wave it makes me jump way too high and it's not possible to slide back.
Try it at lower speeds first to get a feeling of how to jump and stick in the bord. When you feel secure and then try it at higher speeds.
If you wanna land vulcans and later on spocks then it help to go really far downwind, to straighten your front arm completely(while keeping the sail sheeted in with your back hand) before the jump. This keeps your sail in a better position while sliding backwards, so that you can pull it forward easier and not fall backwards with your sail. Also lean a bit backwards and keep the front leg straight while the back leg is bent with almost no pressure on it. This gives you more explosiveness when popping the board.
Personally i would go for the mast when shifting the sail, it's probably easier. As soon as you're able to rotate the board don't make the mistake of not thinking about your hands. Just grab the mast right after the jump, while you're in the air and pull it forward towards the nose while sliding backwards.
Good luck