My main primarily heals in Frontline's and when its just you on you're own its difficult although I have found people really do not want to switch to that role especially with the fact Cleric Stance has been removed. That aside all I can really suggest is put your AP points into Enhanced Vit, use Vit accessories and so on. If the other alliances have extra healers they should be joining to assist you..

Oh and from personal experience I have found if you can party with 2 WHM's with yourself as SCH that is the ideal setup (but if its 4 -5 healers if you're on a base then its pretty impenetrable). Don't give up though its hard being a healer in PvP, but you'll settle in soon enough.

Good luck!