sheep the brontors, and they are still spikey, but at least they won't do normal attacks. You can use abilities like dragon power, and fire line attack (red dragons) and they won't damage you.

You can also Helplessness them to make them easier to kill, or pygmy. Ball lightning though is probably the best choice. It's the strongest rage ability for a mage (maybe mana accelerator.)

Great idea. I also noticed something peculiar. Sometimes damaging the brontors from distance may cause the spikes to activate if there is a troop nearby, friendly or enemy. In a few cases those were enemy troops and the attack did damage to the brontors and to the troop in the neighboring square through the spikes. Funny :)