this is what I do: (sorry for my bad english I hope you understand)
I pick the piece that is broken, and with a lighter I heat the bottom of the lipstick, and they glue back together. with your fingers you can reshape it. it's important that the bottom really melts a little bit so it really gets stuck to the lipstick you still have. then you put it in the fridge.. wait some hours.. and it should be as new.