Howzit LB?
Had a few thoughts;

If your patient's reaction is actually to THC and THC only, this should be do-able.

(Li'l background for anyone wondering what we are on about.
CBN is an oxidation, degradation product found in weed that's way past it's prime.)

If that's really what you are after, it seems a good start would be to allow the plant to get well into senescence before harvest.
And then expose the old, browned, buds to heat and light for several months to a year.

I've recently had the "opportunity" to sample some forgotten stash.
It was mostly CBN
It had no elevation to it at all, just makes me feel tired and dull.

There are >60 actives, in varying proportion, in the raw resin.
He may be reacting to some, many, or all.
That won't be an easy call.

If it is, indeed THC alone, we need to see how he reacts to say, THCa?
It's not psychoactive until you knock off the carboxyl group.

Grow high THCa strains, harvest too early, and store at low temperatures.
Extract the oil an near freezing and store under refrigeration.
That should give you buds that are predominately CBN, yah?
You could formulate with soy lecithin to enhance the bio-availability and keep the actual oil content low as well.

Won't get him high, and he may be able to tolerate it, but if THCa is not as medically beneficial as THC, why bother?

I may have been reading about this patients reaction on a different board.
It made me wonder how well purged his oil was to begin with?
What solvent(s) was/were used?
Was it then winterized and cold filtered?

I mean, If he is actually reacting the the waxes or traces of solvent, that, we can easily fix!

Still thinkin' and readin'.
Type atcha later,

Weeze