When the clew sinks on me I swing the back of the board around under the clew of the sail, the board does all the heavy lifting for you, and in a couple of seconds the clew is back up on the surface. The only time this happens to me now is when I'm rushing a waterstart (like when a wave is bearing down on me or I'm getting swept downcurrent and downwind). If I take my time it doesn't happen.
Don't forget that once the sail is clear, you can hold the boom in one hand and the back footstrap with the other, this allows you to get everything in position ready for a gust. When a gust hits the clew will lift right up, and this is the signal to grab the boom with your other hand, back foot onto the board, bend that back knee so you're doing a one-legged squat over the board while sheeting in, and then you're up.
Regarding footstraps, wave sailors tend to have the front strap well forward, Polakow has his well forward of the production holes. I find it helps when in marginal conditions, weight forward means you can be in the footstraps when off the plane for a couple of seconds. I go for the front strap just as the board starts to plane, then the back strap when up to speed.
Deep water starting is THE most essential skill to have when wavesailing... there's no way I can uphaul a skinny board in waves, but a good waterstart lets you get out of some sticky situations. Good luck, waves are a totally different animal to flat water