A beautiful early spring day,
Not much wind though

In Finn dinghy sailing that is referred to as a JC strap. Finns have a shock cord that runs through a block on the bow and back either side of the mast and attached mid boom both sides with a bit of tension. In light days as the boom is eased the tension in the shock cord pulls and holds the boom out. Does not act as a preventer though. It would be feasible to run two separate ropes through blocks and control a preventer from the cockpit in small yachts.