Please do tell us how you get on. Even better video it for us!! Teaching 'tricks' is such a fun way to interact with your horse, and if you can't do it it doesn't matter a hill of beans because it's just for fun
I can't say I'm a huge fan of trick training unless you 100% know what you're doing, don't use food rewards and plan on keeping the horse for the rest of its life.
I've known too many people and horses that have been injured as a result of silly and 'cute' horse tricks
Reading through previous posts, I can't not say, it doesn't seem that anybody has had a personal experience that has backfired on them, I'm training one of my horses to do the same thing actually, and I would suggest waiting to find somebody who has actually had personal experience to listen to their opinions. All the could possibly, might cause this, might cause that is to be taken with a grain of salt. You know your horse's tendencies, and how sensitive he his to making bad habits, so relate everybody's input to your horse.