You will never have as good of a PvE spec if you take some PvP talents. I would focus on survivability talents over anything else since everyone goes straight for the priest in PvP.
The biggest problem is the points you put into the holy tree. Improved healing, Divine Fury (and Spiritual Guidance if you go less than 31 points in disc) are REALLY important for PvE healing. On the other hand, Spell Warding and Blessed Recovery are really good for PvP... if you are going heavy disc then you aren't going to get both the PvE and PvP talents in the holy tree.
Edit: Something like this
http://www.wowprovider.com/?talent=1121 ... 5510303d5s is the best I can come up with. Maybe move some points from Holy Specialization into imp renew. I don't have any experience in PvP as a priest so I'm not really sure which PvP talents are more important.