The work I was doing regarding this got parked for a while so I haven't had any progress on a solution.
IIRC The solution we were heading towards was checking this outside of the policy by confirming, via data in the JWT or auth DB tables, that the subject has access to that particular Owner ID. Alternatively some sort of solution involving dynamic policies that are generated and saved for users/owners. But I can't say anything concretely yet unfortunately.

