To frag my colt I make straight cuts through it on the branch, just like most leathers. Then to attach it I will put a rubberband on it just tight enough to hold it down. If it is too tight it will just cut through the coral over the next couple of days. You could also use a wooden toothpick to hold it into place, or a combo of both a toothpick and rubberband. I always put the frags in a very low flow area so that it will want to attach. Make sure you do this in a bowl outside the tank, because they put out a lot of slime.
Good luck.