Ahhh, fun fun. Also a great experiance working with spookish horses xD Just be careful while riding, and dont forget the helmet :)
We're currently training my 7 month old filly with the whole 'flinging' movements' & 'saddle pad' breaking. All without the saddle pad.
We use a 10' lead rope, give him about two or three feet. & we make wide arcs before letting the lead rope gently fall onto his body. We do this all around the neck, the back, the legs, the hindquarters. If you let your leg fall against the rump while swinging into the saddle; swing the lead rope there. Don't make any reaction; if he freaks out, let him. ALWAYS remember the less you freak out the less of a big deal it will be for him. Thats why he is on the lead line. Let him run his circles around you until he 'faces up'; stopping, standing still, pointed AT you. This is like when a dog rolls over for belly; hes submitting to you, he wants to trust YOU.
When he starts standing still while you swing the lead rope on both sides, getting slightly more aggressive after a while (not pounding on the horse, but still enough to get their attention of the feeling of 'bumpy riders'). then you know your good to go!
Also for the saddle pad & girth thing we've been using a pillow case. Imagine that! We start tapping it from her neck, all the way down her body same with the rope.
We get slightly more aggressive with this too around the shoulder & back.
my 7 month old is slowly starting to accept the feeling & go with the flow of it now ) although she does move away once in a while.. Just dont 'correct' this by pulling back on them. Let them run, & keep doing it. till they face up, rub their neck, & do it again.
good luck!
EDIT~~~ I've come to realize with the horses ive trained that putting a plastic bag on a stick does nothing to improve them. Each one i've done this too took me months to get them out of fear of the bag as well as any white object. If you want them to get used to bags as well i suggest bringing two or three HEALTHY treats in a plastic bag for him, then when your done crinkle the bag. If it doesnt bother him, then try moving it around his face & neck. If he flips out then back away, and try again tomorrow.~~ Practise makes perfect. Your horse will understand it all soon enough if you just keep repeating it all. :) Remember to take it slow though, dont try another lesson until he's mastered the first.
~~EDIT~~ It's not a bribe. It's another part of learning. I've never had a 'nippy' horse after using this method. I have a TB that had just come off the tracks when i got him a few years ago, and he was scared to death of bags. Using the 'treats' was just a way of gettimg him to realize something GOOD can come of it. I didnt use them each & every time i used the bag, but its just like rewarding a young horse thats done something good. Praise, & once in a while use a treat. Just like a little kid who did something good at school; like in pre-K, you'd get praise & sometimes a lollipop. It's a decent way to get them to remember what they did, plus it associates them with something good.