Before in anyway I harm my reputation here, I want to say this firstly.

EWW bloodelves! Ewwwww! Ewww eww ewwwww! EWW!

Now that is out of the way.. You can't go "Xzin" with blood elves. For pvp, you want to have Will of the Forsaken, and I am sure Xzin as an experienced undead mage/lock/priest boxer would support this to be a key skill in PvP success.

So whatever you roll with blood elves, if you're looking for PvP mainly, blood elves aren't the best for the job. But if you're set on it no matter what and you really want blood elves and aim for pvp. I'd go 4x shadow priest and 1x disc/holy priest!

Would be fun to be honest. :P

And..

Fear Ward
3% of base mana 30 yd range
Instant cast 3 min cooldown

Wards the friendly target against Fear. The next Fear effect used against the target will fail, using up the ward. Lasts 3 min.

Not as effective as WoTF, 1 minute longer cooldown, but will however completely eat fear while WoTF removes it once you are under the influence.

So at the least, get one priest if you are serious about pvp. Don't go without. xD

Viable set ups I can think off..

Priest+4x hunter
2x Priest(One shadow)+3x mage
2x Priest(One shadow)+3x warlock
5x priest (four shadow)

Where one dps could be replaced by a protadin for PvE.

Probably more then this. These all have the ability to do well in bg's, probably not as well in arena's though.