Provide a financial benefit? Or, if he's living off of your family, have a family meeting or write a letter to let him know that you need him to take some first steps towards independence, and you think seeing this psychologist is a good start?
I should add, I am an adult with probable AS and my young son has AS, I have no experience dealing with your situation - but my thinking is that he's content with things the way they are, and why wouldn't he be?