M_Boats: Help wanted

I'm putting a 4:1 outhaul adjuster on my boom, following the Harken pattern, but I can't figure out how to mount the cam cleat, which has a flat base, on the curved surface of the boom. I'm using an existing horn cleat temporarily, but that partially defeats the purpose of quick adjustment. Has anyone solved this problem? Am I missing something obvious? It wouldn't be the first time. Thanks Rick M17 #633 Lynne L