Here's something you could have him do. You could have him wear a certain article of clothing like a baseball cap when he is seeking some pegging play. If that doesn't work, he might wear a specific color to indicate what he wants.

At the end of the day, you two are going to have to come to some sort of agreement on what the non verbal signal will be if he wants this. It could be something as basic as telling you outright or as complex as where he wears a flower on his suit, assuming he wears a suit. As long as you guys come up with something to indicate the activities for the event, you won't have to continually ask. Although I'm surprised that he just isn't telling you what he wants. Do you enjoy participating in this activity?