Ok. First of all you must have some resilience. Minimum 250 will be fine.
Than spec like this:
http://www.wowhead.com/?talent=Iq0rVMdZbxZxx0tr0tmu
But know that this is hunter killer spec and it wont work against every class.
First of all you have %20 more range for affl and dest. spells which will help you a little bit with the insane range of hunters.
The first thing he will do is sending his pet. Just put a CoW and then ignore the pet. Get him in your range, start with SBurn then put Corr, CoW and start draining immediately.
During the combat, your corr and drain life will probably spec nigtfall at least once while the crazy pet will spec backlash at least twice. Use all these instants on hunter. If you have a chance for immo, just do it with a conflg. finish. Else, keep draining and refreshing only Corr. After all these if he's still alive then run away cause no one may kill this guy.