I dont think you should be "sticking" anything to lips as the skin is very sensitive and thin.
The only thing I could think of would be to mix glitter or gems with clear lip gloss and apply it at the very last min, the model would not be able to lick her lips or she would have a moutfull of glitter or gems which if she swallowed them could be harmful. If the gems were too heavy they would just slide off especially if she was in a very warm environment, which I assume you would be.
Sorry but that is all I could come up with. Good luck.
:hug: