Well, you've got to be careful you don't end up suffocating yourself with whatever you try. So if you put something in your mouth to stop you getting at your lips, make sure it's too big to choke on. Maybe a clean, dry flannel would work? Or you could try putting something really nasty tasting on the outside edges of your lips, to dissuade you. I'm not sure what, though - the sort of things you might usually use (wasabi or chilli powder) would only hurt like hell on your poor, broken skin. Maybe something non-toxic but also not designed as food, like aloe vera gel, would be a good bet? Or a moisturising cream? Those things would have the added benefit of helping to soothe your lips.
In the long run, though, you really need some sort of properly-made mouthguard. Go to your GP; they should be able to suggest something (or tell you to go to your dentist if it's something they can help with).