Honestly, just roll a lot. Your body will learn to move in a BJJ way over time because it needs to. I was as agile as frozen molasses when I started and now I have much improved hip mobility, hip control and leg dexterity. It's still not as good as others, but it continues to ramp up. You don't need to be Gumby-esque to do BJJ, just keep doing it and your body will find the grooves and arcs that work.