kingKhandu's Moloch idea is a good one but I'd take it one step beyond, as some of these witnessers are a bit thick skinned and unable to take strong hints.

Therefore, for best results I would think strongly about keeping a gunny sack full of rattlesnakes and when the praising and witnessing starts up, pull out a couple diamondbacks and shout as loud as you can,"TAKE UP THE SERPENT!!", while the rest of the group dances around the offenders flogging the person in front of them.

I have used this method myself on numerous occasions with excellent results.

Yerz,
Tweed