Adult Student and Recipes for Reading

For slightly over a year, I've been using Recipes for Reading (an Orton-Gillingham type of comprehensive reading instruction) on an adult student who is severely disabled. To be honest, he has improved from a first grade reading level to a second grade reading level. Right now I think he's at least a 2.7 reading level. He's just finished blends and some two-syllable words. It takes a lot of time just to get him to learn certain sounds. However, he still struggles with short vowel sounds. Does anyone have any suggestions to help a older student of about 62 years of age with short vowel sounds?

I really appreciate any comments!!