So basically there's a ladder in the Undead Burg that you can reach after you emerge from the aqueduct at the beginning of the level - it's the reached by jumping on top of the aqueduct at the start of the Burg - basically what you want to do is go down the full length of that ladder until your character dismounts it then you want to climb back up the latter and, as soon as you reach the top, move directly left. This should put you on top of the wall. After walking for a bit, you should fall on top of the aqueduct passage near the Female Undead Merchant. Turn around and look out for the Capra arena as you walk back. When you see it, make sure to aim your jump so that you land away from the fog gate but still inside the boss room; this will trigger only the dogs to attack you and Capra will stand motionless as shown in the picture.

how?