Something like this
http://cgi.ebay.co.uk/500ML-HEAVY-DUTY- ... 286.c0.m14
You can buy it from hardware stores too and of course carpet shops,dont buy spray mount or photo mount stuff as its pants and will come unstuck,spray generously over saddle,it will come out like spidermans web slinger,lol,let it go sticky for about 45secs-1min then stretch the leather over working from the centre of the saddle to the edges,when you have about 3/4" left to tuck under the seat spray some extra onto the back of the leather allow to go sticky agin then fold under,try to keep your fingers away from the top surface as youre bound to get bits of glue on your fingers,its easier than it sounds really