When you're first learning how to make your hips "roll," it can be hard to visualize what that exactly means. You likely lift your legs straight out to the sides (so your knees face forward) using mainly the muscles on the sides of your thighs and your hip abductors, because that's how people with advanced jumps look, right? It looks like they're lifting their legs out to the sides. They're not, really, but that's what it looks like, so that's what you do.
Okay, this is going to sound weird, but stick with me for a sec: to train yourself to roll your hips into the correct position, with your knees up, lift your legs to the front when you jump. Seriously. If you have to start with a pike with your legs slightly separated to get the idea, then do that. Yes, your jumps will look funk-diddly-unctious to start with... but keep trying. Lift your legs to the front in the jump, using your abs and rear and the muscles at the front of your thigh. Once you get the idea of lifting your legs to the front, begin working on separating your legs in the air. If, at some point, you go back to throwing your legs out to the sides with your knees facing forward, go back to the ridiculous-looking legs-to-the-front jump. It is all about muscle memory - if you have the flexibility already, you just have to train your muscles what to do *before* you're able to use that flexibility. Hopefully this makes sense :)