I just recently had the same goal. I was lucky enough to find someone that delegated enough SP to me to get me over the 500 mark. Maybe someone will do that for you. There are many people in the Steem family that are very helpful. Of course they will be taking that delegated SP back after you get there on your own, but in the meantime, you will have that slider to be able to upvote more posts. That's what I'm doing now, with this comment.