Ok many people have asked if it can be done, well yes it can. You can cap a lvl 12 npc with 1 lvl 100 hero.Your hero should be at least 325 attack and lvl 100. I actuly did this on saturday march 5, 2011. You will need 1.4mil archers ( you will loose between 650k-850k archers), 600k warriors( will loose about 430k warriors) and 30k pike,sword,workers. You will also need at least 15 war esign.
(15 to be safe)

Wave 1= 100k warriors with lvl 50+ hero
Wave 2= 100k warriors with lvl 50+ hero
wave 3= 100k warriors with lvl 50+ hero
( 1 minute before these hit send your archer clearing waves.)
Wave 4= 119k archers 1500 sword, 1500 pike, 1500 warriors 1k scout, 500 workers.

SEND YOUR LVL 100 HERO WITH AN ATTACK OF 320+ WITH THAT CLEARING WAVE.

Note* if you don't you will not win if you don't send you lvl 100 with 320+ attack!

Once you break through send loyalty waves of 75k archers 23k warriors and 1k pike and sword.

Before each loyalty wave send the clearing wave I posted above to kill the troops in the lvl 12 that have regenerated.

I did this method and lost about 400k warriors, 20k pike and swords, 10k workers, 15k scouts and 670k archers.

Note* This method works people in my allance have tried and captured a lvl 12 using this method.