I think the main thing you need to do now, is ensure you have a failsafe 'forward' button. If you get behind his hip and drive him, he needs to move forward, NOW, and keep moving until you move back to a neutral or blocking position. A horse can not rear when they are moving forward. I would leave backing completely alone until you have a controlled, immediate forward depart when you move into a driving position, and then further, a controlled whoah when you move back to a neutral or blocking position.
Duh. I forgot to add here, once you have forward down, it is the anti-dote to rearing. Now he has the rearing as a habit, every time, and I mean EVERY time he starts showing signs of wanting to go up, you need to drive him forward strongly and immediately. If a horse rears in hand with me, I get after them VERY aggresively (Not physically though, voice and body language all thrown at the 'driving' section of the horse) and normally have a few circles of canter on the end of the lead. Once they relax, I let them stand before tryign whatever it was again.