Use a pair of needle nose pliers, spread the pliers so that they grip the interior of the nut and turn. They also make special sockets that fit those type of nuts, local parts store might have them, or take them to a interior shop.
First I found a nut that would fit snugly inside the hexagonal cavity, then I drilled out the center hole large enough so it would fit down over the post in the center of each of those fasteners. I had a set of CHEEEP sockets so I found one about the size of the nut I just made. Then I epoxied the nut to the socket (just not the drive end - ask me why I include that note.... )
This works like a charm and is almost as good as the tool the upholstery shop has. ALMOST... It has a front row spot in the 'Assorted Tool Drawer'.
Now that you have heard this method - if there is a next time I think next time I will try :