The solution is a minimal footprint interaction, like a coarse-grained document transfer via a pin-hole, a la’ a Biztalk port. Exposing all your data via GET so anyone can read anything they want (modulo security concerns) and then providing controlled writes through pin-hole ports that consume documents and encapsulate the actual update process.
Bingo! Give the man a cigar.
That said, once you’ve done that for a while you will, in all likelihood (I’ve been there), find the need for the client to have expectations about server-side state changes beyond those offered by POST; PUT and DELETE are two very useful expectations.