This post is odd only because 90% of the skateboarders I know do absolutely zero strength training. Their only training comes from skating and the inherent cardio in the sport.
Predominately, I need to have lean/strong legs for jumping motions, a keen sense of balance, and strong joints (knees, ankles, hips).
How can I use HST to focus on the agility, strength, and improve jumping height for this? Ideas?
well HST is Hypertrophy Specific Training... that's not what you're looking for.
I'd do some balance exercises, like dot touches and maybe some plyometrics.
If you haven't already you should check out Renegade Training. John Davies skates, surfs, and works with professional athletes in about every sport imaginable to improve performance.