If you have access to a round pen, I would do some round penning work, again like with the backing, give him a choice, he can work or he can let you put the saddle on. Even if you dont have a round pen you can use the Pony Boy method, I believe its called the circling game or something like that. You use a fairly long lead line and carry a whip under arm, or if he will go from the end of the lead that works too, and every time he moves even a step, remove the saddle and chase him around you for 3 circles. The key to this is to make it unenjoyable, it cant just be let him trot leisurely around you three times, you really need to make him work. Dont worry about taking the saddle back off, as he is learning when the saddle is on he isnt uncomfortable, but when he doesnt let you put the saddle on he gets uncomfortable.