I swap in PvP-focused gear. For me, that's Robes of Transmutation (critical resistance for group), Sanctuary (can be too much healing for PvE, but helpful in PvP) and Chokethorn (mobile lock-on makes it impossible for teammates to ignore the heal). They're all fairly easy sets to obtain. Everything that can be is traited with Impenetrable. (I'm not 100% sold on Sanctuary, because the green orbs make it easy for enemies to know who to focus on first.)
I'll change two skills usually. I swap out Spear Shards for Piercing Javelin. The knockback can be huge, especially for Battlegrounds with objectives. Lastly, I'll usually swap out Warhorn for another offensive ultimate. Too many times I'll be in a 1 or 2-person fight, and I feel like Warhorn ends up being wasted.
It's not perfect. My CP allocation is still primarily PvE focused. But, it's enough to make a significant difference. I've had multiple Battlegrounds matches with 750k+ heals and passable-ish damage.