I've used rubber cement. Spread rubber cement on both surfaces to be
joined, and let it dry. Then press the two edges together, clamp it
or weigh it down. Depending on the thickness or stiffness of the
suede, you probably want to hem the trousers an inch or so longer than
you want them now. Leather tends to develop permanent creases which
will make it hang a little shorter after a few wearings.