The only way to level heavy armor "Faster" is to buy training in the skill.
If you wear mixed armor, you level them at a slower rate than if you wear just one type, because of the way armor XP is handled.
Any idea if the training is set to
Morrowind's as much as you can afford system, or
Oblivion's only five times per level system? I figure it's the latter, but realistically, if you have the money and the time, you should be able to get as many lessons from trainers as you want.