How about this : Wild Shape into an Invisible Stalker and then use an Eternal Wand/Scroll of Hunter's Eye. Backstab him to hell and back
And on the off chance he's prepared for a sneaky druid, make sure you've got all those nice Wild Shape feats to speed up Wild Shaping (or Planar Touchstone) and then Wild Shape into something very unpleasant. My current Wild Shape Mystic Ranger will be doing the Fleshraking Tango in one more level, and IMO it won't lose it's touch even at 20 with the broken wonder that is Venomfire. Hell, you've got feats to burn...take Searing Spell just to be sure in the event he snags a form/spell to be immune/resistant to fire, especially if he knows how wicked Venomfire is.