Just call (512) 389-4505 answer the questions and they will mail you out the cert. I have a lifetime license and that is how i do it plus I get my crane permit at the same time.
I also get my federal stamps this way as it shows on the license that it was purchased. You still have to sign your stamp when it comes to you in the mail. I always put my stamp on my Colorado license because I have one going back to 1975 with all the duck stamps since then. This makes it easier when you have to show a rookie game warden.