Ed Kranz has a good time lapse video on his blog showing how he back riveted most of the tail cone skins. http://www.goodplaneliving.com/tail-...in-full-swing/
I mostly followed his example except I think I just stood on a stool and reached over the side skins to back rivet the bottom skin rather than climbing into the tail cone to reach them. I switched to a bucking bar for the bulkhead rivets and the side skin to bottom skin rivets.
You could also just put the tail cone on its side and use a riveting partner to do the bottom skins. That's probably how you'll have to do the side skin to bottom skin rivets anyway.