Well first of all, I haven't met any drummers who started out with a "quick foot", cuz it definitely takes time. But one thing I started doing, which really helped was... while i'm at home, school, or work, i'd sit down and constantly do a "tip-toe" - to - "ball (of foot)" continuously. Getting faster and faster.
You'll notice when u're back on the drums, how more confortable it will feel to do a double (even tripple) beat. It will take time, but you'll deffinitely see improvement.
I've moved on to keyboard, so I don't play drums like I use to, but that excersise did me a lot of good.
hope that helps...