[video=youtube;s92zbteKHQg]http://www.youtube.com/watch?v=s92zbteKHQg[/video]These guys do a bag with a back protector in them http://www.evocsports.com/en/evoc-technology.html
The vid is a bit misleading hey, but i think they are trying to show that you can wear the protector with out the bag cargo section attached which assumably just zips on.the vid is a bit cheesy and I'm not 100% sure how you use the back protector with the back pack (ie, whether is it built in but removal, or you wear the back over it so effectively two layers).