I agree with May! My 11 year old son acted the same way between ages 3 and 6. He was in special needs prek until he was 6 and then we tried regular kindergarten with support. It is so hard to break them once they learn these innappropriate behaviors. I put my son in every activity i could find where he would be mainstreamed with NT kids. He then started copying NT kids behavior. Today he is ok socially. We have no stims hardly ever. This year he is in a class with children that have learning disabilities but not autism. I am not a fan of the ASD classroom because of this reason. My son was LFA and now he is considered high functioning in the last 5 years. I also have a daughter with PDD and she has been in regular classes with support since special needs pre K.

Is there any possibility of him spending some time in a mainstream classroom? If he's that interested in imitation (which in and of itself could be a sign of emerging social behavior) perhaps more time with typical peers could result in him imitating better behaviors.

At the time I thought that our son was trying to see how it felt, or what it was like, to do these things, like walk with crutches, which he would make out of things he would find around the house.

Here is a very interesting article that will help explain this behavior http://psychcentral.com/news/2013/04/09/autisti... The child is not seeking attention. This is part of his learning process. I also read an article on the importance of US imitating our child with autism. They will pay closer attention to you, and then you can encourage them to imitate you.
There is a function behind every behavior. It's up to us to figure out what that function is, and provide a safer, more appropriate means of meeting that need.

My son did the same things in Head Start and Early Intervention. He would imitate children who needed crutches to walk, and individuals who had tics. My son would come home from school and set up chairs with his stuffed animals and actually re-enact his day in school, except NOW he was the teacher. I could actually SEE what had happened that day in school, and sometimes I was really upset at what I saw and heard.