I would just use a client that filters ads. You can't force ads without proprietary software
Discussion
Yes you can, at the relay layer.
What if clients filter them out?
1 in 100 posts from a random keypair with branding. Any pow by clients just adds to the fee charged by the relay.
Very difficult to filter ads at the client layer. It’s whackamole at best and that’s only feasible with money to hire people - you can’t automate against all the methods to advertise.