So after much debate I decided to mount the frags on rock rubble. I had originally planned on mounting them on frag plugs but I had a ton of rubble left over and found they were relatively easy to place on the rocks in the display, since I hadn't previously drilled for plugs. So here's how I went about giving the frags their new home.
Rock Rubble. Some of this was left over from when I purchased the Marco Rock that's in the display. There was quite a bit of rubble I saved from the bottom of the boxes.
I used Loctite "Goof Proof" Super Glue. It has a slightly longer working time. I'm not sure if it's a true gel type but was definitely easier to work with than regular liquid super glue.
I see why they call it a Green Slimer.
I lightly blotted the end I wanted to mount the frag with some paper towels.
I then placed a few drops of the super glue on the rock rubble and also to the bottom of the frag itself (not pictured). It was difficult to take pictures and be quick about mounting the frags but you get the idea.
And finally I placed the frag into position, held for a couple seconds and voila! The finished frag.
I had also set up a couple small plastic containers which you can see in the background of the pics. I put a small amount of tank water in the container so after I was done mounting the frag I could submerge it to keep the coral wet and it also helps to speed up the super glue curing time. The whole process only takes a minute or two depending on the working time of your super glue.