S.Screams might have hit on a solution, Muf' - try bribery. That or bacon...guys love bacon. As a last resort, right before the Trick-or-Treaters arrive, you could use Terry-Thomas' answer to the problems he faced in Munsters Go Home (1966): "Bash them on the head, with something jagged!"

Not only would that make Jerry and Joe see the light, they'd be all set to go for the party...

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Mark McG.
It seemed like a good idea at the time.