I need to fiddle with this a little more to see how well it will hold up, but here's what I just quickly tried:
I started with a 6" tile template that wraps around the foamcore. Before gluing down, cut small slits in the face for the post supports to go in. I basically cut one edge of the anchor glue spot area open (one of the edges NOT on the edge of the tile...) This let me slip in a special connector that the post would fit into. The fact that the edge of the tile template is 1/4" and the tile is less thick than that is actually helpful. There's a little space available to wiggle the connector into.
Don't glue the face of the tile down. Or, at least, only glue the middle of the face down - I don't want glue at the edges of the face. Glue the flaps down underneath.
It seems to work OK, but I want to try it out on a couple tiles, and I want to come up with my own post template too. Sadly, I threw out my back this morning, and it's getting uncomfortable to work for a long stretch...