A wrap or 2 of adhesive backed aluminum tape (real duct tape) around the work or on the ends of the chuck jaws.
Pet peeve - there's no need to quench brass to anneal it! About the only things you're likely to run across that are affected by quenching are iron alloys & a few aluminum alloys; everything else can be cooled at any rate by whatever is the most convenient, keeping in mind that quenching can warp things.
Roy
