I don't know how to do it in Gnome either, but I know it's different. Duh? What i mean is it saves session in a different manner than KDE. (or at least used to) Some people were complaining about saving a session with some app running and then wanting to get rid of that app starting at some later time was difficult (if not impossible). That may no longer be the case as I haven't seen it for a while.
That said (I don't use gnome so you will have to research for yourself), try