I'm not sure that concrete without engineered-in rebar and expansion joints would hold up to repeated frost/thaw cycles. That having been said, I would think that pre-fabricated buttressing assemblies could be used to make sandbag walls stronger while using fewer bags than would otherwise be needed. My parents and I used some of the neighbor's pier sections for buttressing (they had not been secured, floated up on the lawn, were not damaged by use, will be returned, and would have likely been destroyed had we not used them, so there's no issue of theft), and they worked well, but most people aren't going to have pier sections readily available; other types of reinforcement could be fabricated cheaper.
Im sure if I followed the money, I would find an answer...