Thanks for your question! What a wonderful thing you are choosing to do, working in this beautiful boys Son-Rise Program!
At times, we will have a child who is asking not to be joined. There are two things that are the most effective in this situation.
1) First experiment with the way you join. Often, our children are very specific about their isms and they can be very easily interrupted if we are too close, too intense, or too loud as we join. Make sure you try joining from a distance (at least 4 feet away) and even try turning slightly away and joining in a quieter, less animated way. If he stops telling you not to copy him then keep joining in the way.
2) There will be some children that will still continue to be conrolling around you joining them and tell you to stop, even when you have experimented with being more low key. In this situation, you want to be excited to give them control and show them how user-friendly and trustworthy you are. At the same time, you could join in a way that has a similar element to their ism but is not exactly the same.
For example, I once worked with a boy who would walk around the playroom reciting the story "The Ice Queen" as he looked at himself in the mirror. When I joined this, he told me "Don't copy me". At this point I celebrated him for telling me, sat down and whispered the same words as him. Even then, he told me "Be quiet". Once again I celebrated him and then got a piece of paper and a pen and wrote the words he was reciting down on the paper while being silent. I had fun imagining the story in my head with the same amount of drama that he was creating from reciting. This he allowed me to do no problem! As the week progressed, I could slowly get louder and more exact as he became more flexible.
If this boy is conversational, you could also explain that you are doing what he does because you love him and love to be interested in the things he is interested in. You are his friend and that's what friends do!
For the activity where he will have you repeat certain phrases, give him control and enjoy doing that with him as that in of itself is the ism.
For the last question, the answer is yes!
Have fun! We would love to know how it goes!