Just reach up with a boathook and grab the halyard, pull the slack down around the horn of a cleat and then take back the slack on your winch. That will actually force the headboard downwards and stop the flogging.I was thinking of steps at the base, however there is a fair bit of junk already attached to the mast (three winches, 3-5 cleats, etc).
And you probably need a longer halyard if you say yours is a little short.
Taller crew only sometimes helps. They start to whine when you force them to dig into small lockers for bits and pieces!