Before you play everyone in audience sings “The Twelve Days of Christmas” give the rules.
Each of the twelve days of Christmas corresponds to a month of the year. Eg. First day = January, second day = February, etc.
When the verse corresponding to your birthday month is sung, you stand up; when it’s finished you sit down. You *also* stand up whenever the gift for that day is sung in the chorus.
For example, my birthday is in March, so I stood for “On the third day of Christmas my true love sent to me three french hens” and ever after whenever we all sang “…four calling birds, [stand up] three French hens [sit down], two turtle doves…”
Once you get four or five verses into the song, you have people popping up and down like crazy.