yeeaaahhhh !!!
I think I found a magic trick! ok ok I do not know if this miracle has been found.
To add highlights with an object that is in the field of the camera, but that one makes invisible with the emissive materials.
If it helps someone :)
http://www.screencast.com/t/Et4qs9qiY
Antoine
It's cool what you can accomplish with emissives, for sure!