Anyone have any other ideas of getting him to recreate the feeling of being high without allowing him to light up?
Three things I'd like you to consider:
1) If an employee is getting high on the job (or is arriving at work intoxicated) and management doesn't intervene, you're automatically voiding some of your insurance policies. If anything happens to this actor (or happens as a consequence of his actions), your company may end up having to eat the consequences without any assistance from your insurers. This isn't just about his health and well-being, and that clause isn't in his contract just because your managers disapprove of pot. This is a serious financial risk, and one which can be easily avoided.
2) You don't owe this guy anything. He's not entitled to perform, he's not entitled to your support or assistance, and he's not entitled to have his ego or feelings protected. You should make every reasonable effort to protect and help the guy out, but if the thing keeping you from firing him is a worry about hurting those feelings, this is something I would urge you to get over. His drug use is only your problem insofar as you're prepared to tolerate it without cutting him off.
3) The only thing worse than an untalented actor is an inconsistent actor. A bad actor, handled properly, will not ruin your show: you park them in the back row, you give them few lines, you keep their part simple, you can manage it. An inconsistent actor, on the other hand, is by-definition
unmanageable. If his performance varies that much from night to night (sometimes it's transcendent, other times it's abyssmal and--if he's dropping lines and ignoring blocking--may even be violating not only his contract, but the director and author's contracts as well), and
especially if there's a deep-seated and unmanageable problem underlying the inconsistency (like, say, substance dependence), you will only be able to assert very, very tenuous control over this actor, his performance and the situation generally.
There is no good solution here. Someone gets hurt and bruised no matter what you do.
But as a stage manager, you are ultimately an agent of the producer, and a large part of your job is to protect that producer from potential liabilities like this. (It's not your job to personally get this guy off dope. It
is your job to kick this upstairs and alert the appropriate people within the company so the situation can be handled appropriately.) And sometimes, in this capacity, you need to suck it up and ruin someone's life.
It sounds to me like this may be one of those times.