With the xenia, you can usually get frags just by laying a chunk of rock/rubble where it's touching the current colony. The xenia will quickly attach and grow onto the rock, then slice it free with a razor blade (or just tear it off if your impatient)
Zoa's can be fragged about the same way as above it you have a good sized colony, just arrange rubble so it's touching, remove a couple weeks later with zoa's attached. For more active fragging tips on zoa's I'll leave that to the people around here that are better at it than myself....
For finger leathers, it partially depends on what specific kind of leather. Is it leathery and tough feeling to the touch, or slimy/squishy feeling?
The tougher feeling ones are very easy. Slice a section off with a razor blade, scalpel, or even scissors. Then loosely attach the frag to a small rock with a rubber band, OR, stick a plastic toothpic through it and gently rubber band that to a rock (so the toothpic is holding the frag in place with the cut tissue lightly touching the rock), OR with or without the toothpic, gently place the cutting between 2 small rock chunks and loosly put a rubber band around the rocks so they lightly pinch the frag in between.
For the slimy feeling leathers, pretty much the same as above, but much more carefully. Best to wait for some practice before trying that.
Also, IIRC, if you look around their site,
www.garf.org has some nice how to's for fragging.
For any of the above, it's best to have the fresh frags in a place where they get some deccent flow, but not enough to blow them off before they attach solidly.