The only way to stop queue syncing is to:
- Add a stacking debuff for not taking a queue.
- Fill more than one battleground at once from the same queue.
- Stagger queue pops so that people who are queued together can’t tell if they are in the same instance or not.
- Full randomized cross faction queues, like Blitz and RBGs. (This will also allow the match maker to spread healers out across both teams.)
At the very least, adding a debuff is the easiest and fastest solution, it already exists for other queues.