One way that may be possible is to target and have someone else kill it, that is if they can even attack while you have it targeted. I can confirm this won't give xp and you'll get the drop from my experience with killing abby demons, however I'm not sure how this works with slayer/quest creatures. It is entirely possible that this may not count as a kill that triggers this part of the quest, much like how we can no longer do slayer by purely recoiling as the kills won't count.
If you want to continue in trying to recoil consider purchasing Ancestral Spirits Aura. Costs 50k Loyalty points, and hits rather nice if you have a decent prayer level or at least I believe prayer influences how it hits. Would certainly help kill it faster.
I'll see what I can test in the next few days when I have a couple days off.
Blackston is a Naabe.
22-Jan-2013 16:45:03