I use fishing line to attach my xenia. All you need to do is just tie it down to a piece of rock. You don't need to "sew" it or anything intricate like that, just tie the fishing line about half way up its shrivled stalk to make sure you get a good hold, tie it down and put it in your tank where there is a low flow area so it has a chance to attach. In a day or so it will attach and you will be good. No need to remove the fishing line afterward. The coral will grow around it.
Just a few suggestions. Use a new clean and sharp razor blade. Try to make as clean of a cut as possible, and I always dose my tank with iodine after. Iodine helps corals heal.