Just Krazy Glue the bolts in place. Krazy glue comes off easily with acetone so you can remove it when you eventually need to. Unless you need to change your seat height or angle frequently this will work. The would be thief isn't going to know what he is up against and will quickly move on to someone else's bike. All the other methods can be defeated with a cutter but bike part thieves aren't in the habit of carrying around acetone. I would use this strategy myself except my seat post doubles as a pump.