Some participation encouraging patter that one of my bands used goes roughly as follows: After your charming intro to the song, what it's about, whence it came, etc, your usual method of Selling it before performing it, continue as follows:
1. Well, now on this next song, we need you all to sing on the chorus because ______________(fill in the blank with a real good reason depending on the tune such as for a wassail: "everyone in the town went door to door singing this chorus, and accepting a cup of wassail, and then the folks in the house joined 'em, until the whole village was in the streets, drunk as skunks, and we need you to be our whole drunken wassailing village! There aren't enough of us on stage - we need your help! And it takes a whole village to raise a wassail!!!" or, in an underheated hall - "You need to sing along because getting all that good oxygen into your system will really warm you up" You get the picture - something germaine, and irresistable, and with a bit of humor where appropriate.
2. Now, we'll teach you the words first, then the tune. ( go over the chorus line by line, and ask them to repeat after you)
3. Then sing the chorus line by line and have them follow; then sing entire chorus slowly.
4. Then stop and say, "well now, we have a rule, that we must see at least 50% of the mouths moving, and we'll just keep teaching you until we do. But do you know, a lot of people are afraid to sing because some terrible person, a teacher or someone else in authority told you you couldn't sing. Can we see a show of hands of those of you who were told this? Oh my, that's so sad. But, you know, that just isn't true. Most people can too sing - But even if you can't - it's your NEIGHBOR's Problem! NOT YOURS!!!
5. That last line always gets a laugh!! Make sure to ask them if they're ready, does anyone need to hear it again, then go for it!!!! You'll have them singing along heartily and (figuratively) eating out of your hand.