They're mostly non-technical/marketing people, but yes that would be a solution. I try to solve the issue "behind the scenes" so for them it "just works", but that means building all of these extra measures.
Would it make sense to advertise to the more technical minded a discount if they set up an IP whitelist with a tutorial you could provide ? A discount in exchange for reduced costs to you ?
The right solution is to be registered at Cloudflare, but then getting the customer reach the guy who handles Cloudflare settings (a few clicks) is the hard part.