I don't have Personal Hotspot on my iPhone 4 iOS 7 test device, but I'm guessing there's no way to enable this in control center. I think this would be a welcome addition. I'm constantly turning it on and off on my 5(mainly because it times out after a few minutes of inactivity) I would use it more than the Do Not Disturb one or even the Flashlight. It would be nice to customize these. Not holding my breath though.