Prevent Pre-Game Spawncamping in the Battle for Wintergrasp

I'm referring specifically to people (of either faction, either attacking or defending) creating a group to kill everybody who spawns in when the battle starts.

Timing is hugely critical for a successful Wintergrasp campaign, especially at the beginning, and forcing people to respawn wastes significant amounts valuable time and provides an inordinate advantage to the side that does it. From a tactical perspective, it's stupid to not do it every game if you have a group willing to help you. This damages the competitiveness of the battleground and rewards cheese.

Possible solutions:

Remove everybody not in a Wintergrasp raid group from Wintergrasp immediately as the battle starts
-probably the cleanest solution; neuters this tactic in a simple way, expediting the timer that already exists to teleport people out of the zone

Give immunity to people who spawn in at the start of the battle for x amount of time (~10 seconds or so)
-targeted anti-cheese; works well for this purpose (possibly even better than the first, because it also blocks traps etc), but may be a bit too "custom" for the liking of some, and may be harder to technically implement,

Do nothing in-game, but make the behaviour bannable
-worst option in my opinion. while cancerous, banning people for something that was not previously bannable sets bad precedents and diminishes trust.

Feedback appreciated.