Maybe eat a "big" snack before going to bed? That way, your internals are active with digestion and then the digestion of the food will keep your body away enough to get to SP (I know some people can't eat before bed because it causes them to stay awake)

Also, mantras or counting breaths can keep your mind awake enough to get into SP without falling asleep. I find that sometimes, even when I'm not that tired, I'll conk out after a few mins. Oh well, haha