There is a lot going on here, my opinion is to treat
the self induced vomiting, and cut down the saturated fats, natch
Not going to happen overnight.
Back in the 80's, lemon juice therapy was introduced,
look into that for the vomiting.
He will only self administer, there is little chance in tricking/forcing him.
Cannabis can only work if its ingested, no matter the transport method.
His behavior needs to be gently modified to allow his medication dosed,
often happens while you least expect it.
Have low dose medicine available to him, without the stress of a dosing event,
and he may accept it on his terms.
Keep tabs on his ingestion and hope for the best.
"So we're just done with phrasing, right, that's not a thing anymore?."