There are several ways you can do this. You can cut the cap off the column, and the column will grow a new cap, and the cap a new column, or you can slice pieces off the cap and they will grow.
Some folks use tulle netting to hold the frag in place on a rock until it adheres, I've used a shallow plastic container (like Gladware) with a few holes punched in it, place the frag in there with some coarse substrate (live rock rubble is good for this) and either place it in lower flow where it won't get blown out of the tray, or put some netting over the top with a rubber band and wait for the frag to attach itself. You can then affix that substrate to a larger one - like a rock or larger rubble piece.
HTH
Jenn