We use a preventer line that runs through the boom to the companionway winch and rope clutch. On the end of the boom it is fitted with a snapshackle. We have two lines with spliced loop in each end that run from forward cleat, outside of all the stanchions, to midships stanchion where they are held in place by a soft shackle, one starboard, one port. To rig you pull out the preventer shackle to the midships loop, snap it in, winch the line tight and done. You only have to step out of the companion a little ways.
My experience with boom brakes on smaller boats is that they are hard to set up properly for the given conditions. We just bring the boom back to midships and then Jybe.