Take some younger dragons and give them levels in rogue. If the dragon is small enough, hide and move silently are awesome. Sneak attack can be truly deadly. As a backstory, have a small group of juvenile white dragons whose mother was slain soon after they were born. Each have some levels in rogue and together they work to bring down much larger prey. They are truly cunning, using incredible surprise attacks and flanking tactics that catch people totally unawares.