You may want to grab yourself a copy of Anthony Calfo's Book of Coral Propagation
. It's actually pretty straight-forward to frag
a leather.. just cut around it about an inch or so thick (so you end up with a donut-like shape), and then cut that into 1"x2" pieces. If you have reef putty you can make little discs out of it to use as a base for attaching each frag
There are a few other details that I can't remember right now like stuff to add to help the leather heal, and keeping good flow etc.. it's all in the book.