You've got all these scrap lipsticks around that you either didn't use, used too much and now they are just a nub or didn't like the color to begin with and they're littering the bottom of your makeup bag. If you leave them too long I guarantee they'll be leaving streaks on your good clothes and melting to the sides of tube where you'll never get them out.
Use them now! Don't make this another DIY disaster where you read something, think "that's a good idea" and then go on to eat pork rinds and watch CSI. Grab all your lipsticks. Yes, now! This is easy. We're not going to over complicate it and we're not going to use anything difficult. All you need are your old lipsticks, some butter or oil, a baggy and a microwave.
Load up the baggy with the colors you want and nuke them for 30 seconds. This will liquify the colors together. Feel free to remix and add more of one color or another. You''ll want to use one of the old caps to stick the baggy in so it will mold the lipstick as it dries. Once it is dry, pull the bag out and cut to a preferred size. Use one of the old lipstick bases to insert your tube into.
Voila! You are a magician's apprentice! Now apply the lipstick and make sure to give yourself a kiss.