Make him sell weed for you and give him a revenue share. Probably the only 'niche' he has some knowledge in according to your brilliant description.
In order to get him to change you need to interrupt his pattern and replace his unhealthy habit with something 'better'. Without him WANTING to change this is going to be a loosing battle.
Depending on how good of a cousin he is and how hard you want to try, go take a trip with him for 3-4 weeks. Camping in the wild or somewhere you guys can't readily access technology. Find out what pleasure he derives from his habits. Try to introduce new habits to him. Get him on the Paleo diet (I've got a hunch that more then 50% of all problems are due to bad diet these days. YES, I'm completely pulling this out of my rear end. It's my theory... bite me) and see if his behavior changes. Go exercise with him. Do some yoga... teach him how to meditate.
Take him sky diving. Take him with you while feeding the homeless, working on habitat for humanity or help build a water well in Africa somewhere. Give him a reason to LIVE his life and inspire him.
If he's playing total domination show him how that relates to the 'real' world and how he could build his own business eventually dominating real life.
Just remember, don't blame HIM if you spend months and months trying to help him and he goes back to sitting on the couch smoking weed playing on Facebook.
He didn't ASK for your help...