RPC over HTTPS connecting to a cluster of back-end only servers

I have a client who wants to connect RPC over HTTPS to his two node Exchange cluster with the servers set to being back-end only. I know this isn’t the recommended or even proper solution but he swears he’s been told it is at least possible. Anyone have any tips? Or even an explanation why it _can’t_ be done? (or realize why it _shouldn’t_ be done but my searches for an explanation haven’t come up with much.)