Hi Andy, and welcome to SR.
If you wouldn't mind giving a little clarification, I'd appreciate it.
You say your cousin is 30 years old. Is he court mandated to go to rehab, or just what are the circumstances? He is a grown man, albeit a spoiled one from your description.
Your post implies he has done traditional rehab already. So essentially he has the tools to stay clean, but chooses to remain in active addiction. That is his choice.
Rehab is not a miracle cure, nor will it do any good for someone who's just not done with active addiction.
Rehab is only as successful as what the addict puts into it.
I encourage you to read the sticky posts at the top and educate yourself on addiction.
Get yourself a copy of the book "Codependent No More" by Melody Beattie.
See if there are Alanon or Naranon meetings in your area for face-to-face support among those who understand.
Please keep posting and know that you are among friends.