I add glycerin to my shaving cream, too. Much more than anybody else suggests, though. Maybe a quarter teaspoon? I've also tried glycerin with rose water. Here in Belize my pre-shave often suffers because I don't have running hot water and so my face suffers. The glycerin with rose water in the shaving cream or even as an aftershave really, really helps. Plus, I only shave once a week here.
I'd like to try adding some coconut oil.