But the thing is, you don't need those ropes at all!
First what you do:
1) Make a fist, and touch your horse's nose with your fist and then reward him with a treat. After a few days of that, see if he'll search for your fist and touch it -- as if it's a target. When he does, pat him and reward him with a treat. Now, once he associates your fist with a target, you can start to move your fist between his legs and he should follow and hit your fist with his nose -- to get the target and treat!
2) With this in mind, then you can start to ask him to put his head between his legs and he will lean back naturally -- then you get the bow!!!
3) After you teach him the bow, lay down is just one simple step after. It's really natural for a horse to lay down so you could probably just move your hand so it forces him to lay down to get the target and there you go!
Now, while you're teaching him his tricks, teach him the words to them so he will be able to do his tricks on command!