Here's a drawing from the assembly/service instructions that I posted a while back:
The 'fastener' shown below the baseboard is a T-nut with threads to fit the cap screw. You'll need three of them. I don't know the thread size off the top of my head, but could check if you need that info. T-nuts may be available at your local hardware store. You need to drill a hole for the T-nut to fit into. The flange of the T-nut is on the bottom of the baseboard to keep the cap screw from pulling through the baseboard.