Lots of leg lifts. Also if you don't already try jumping off of a panel mat to catch the bar to get more momentum. Also wait till you get to the top of your swing ( when your legs are completely extended and jerk you legs up hard.
Lots of abs conditioning! If you have a pull bar try pike hang and hold for 45 seconds x 3. As it gets easier, try to challenge yourself & increase the time. Also leg lifts working your abs and twitch muscles. (but don't swing, keep your knees straight no matter what & try not to let your feet go behind you!) Hollow body holds, planks etc. My coach also has us do leg lifts with light weights. Maybe work 3-5 glide swings in a row with or without weights too making sure you extend all the way. Hope you get your kip faster!!