I did this yesterday. First time was utter fail, then I tried a new tactic. I am a powertech tank, so Skadge got initial aggro. When he was down to about 3/4, I taunted, then he would grab aggro back after about 10 seconds. I just rinced and repeated until Skadge died, and I still had over half my life when Zale was at about 20% of his. I had to use a consumable during all this too, keep in mind. If you are a powertech try that. If you are a merc then try speccing heals and just keep Skadge alive.