Jules, have you read Lost At School? (also by Ross Green) It was helpful to me because it did include a lot of scenarios (not sure if they were real or not, but it always helps me to see something in action, and this book had lots of that).
My only other suggestion might be to get a little closer to the action, and then as you see the friend getting irritated, use CPS with the friend, right there for difficult child to be a part of. I am thinking that friend may say that difficult child is being too controlling for friend to have fun, and difficult child can jump right into the brainstorming phase...what might he do to change the situation, etc.
It takes time to get this down, and sometimes I still have to stop and think how to go about it, but kids do catch on quickly that you are trying to help.
I have also found that walking thru this CPS, in itself, helps the kid get around, to some degree, the skill he/she is lacking. It teaches them to stop and work thru a problem...it might not be the way a "typical" handles any given situation, but it does teach the child to recognize there is a problem and to think thru options. Wee doesn't do it for any major issues yet, but I see him (or he will actually say "now, what can I do to make....") use the method in other areas, so I think, in time, he'll be able to collaborate with himself on some real issues. I've also seen him say to his younger cousin "how can we fix it?"
