Institute Corp roles, and only allow people with the right permissions to join a squad to a PC battle. It looks like most people agree on this part.

However a kick function is touchy, and for good reason. Most people, myself included, think that espionage and sabotage should still remain viable tactics, once implementing those tactics actually requires some work and planning. If a kick function is implemented, it shouldn't actually come in the form of kicking the offenders from the battle, not immediately. It should only disconnect them from the clone reanimation system, after which they still have to be killed before they are removed from the battle. They should remain on the TechNet as a blue, an always visible red, or a new color entirely. They cannot be replaced with loyal personnel until they are killed. For reasons I'll explain shortly, I would also create a one minute thirty second spawn timer where all players have to spawn into the game before it runs out, or be automatically spawned in the MCC with whichever fitting they have selected at the end of the timer.

This would allow things to play out in multiple ways.

1. A rogue director brings in a hostile squad. They're cut off from the clones while everyone's in the MCC because hey, it's obvious these guys are hostile. They immediately spawn in, and cause some TK'ing havoc. They eventually die themselves, and are replaced with friendlies. This confusion and the time it takes to get a replacement squad in gives the other team a not insignificant head start.

2. A rogue director brings in a hostile squad. They're cut off from the clones while everyone's in the MCC because hey, it's obvious these guys are hostile. They don't immediately spawn in, opting instead to wait on the 1:30 spawn timer. Now the team has to make several choices. Do they post guards at the base spawns to kill them if they spawn there? Do they hack objectives and give the rogues additional places at which to spawn? This again gives the other team a good headstart on taking objectives and setting up defenses.

3. A rogue director has either several other spies in his squad with him or has several other members of the Corp/Alliance he's "helped" decide they want to switch allegiances. As such his squad is all wearing the right Corp tags. This may or may not go unnoticed beforehand depending on how stringent his Corp is about specifying individual squad members, and how good he is at allaying suspicion should questions be asked. It will probably be increasingly less likely to be noticed as battles grow larger in size. This squad could have the added benefit of having surprise on their side. As such they are not disconnected from the reanimation system beforehand and could potentially waste a LOT of clones before the subterfuge is discovered.

4. In any of these instances, if the rogues can escape being killed after they are disconnected from the clones, they have to be hunted down if the team wants to replace them with friendlies. The hostile team would also need to make sure they don't kill their own agents. If the rogues decide to call in vehicles or run around in the hills, this could end up being a significant time drain on the team, to the point that it might be preferable to simply fight a few men down rather than devote resources to chasing a scout around the mountains or trying to actually kill a LogiLAV that never stops.

So in this system you have varying degrees of work for varying levels of payoff, and if played smartly all have significant ways to influence a battle. Meanwhile corporations are provided with controls to prevent unauthorized access to PC battles and a way to mitigate damage should kicking be introduced, without kicking being a "get out of paying for your mistakes" free card.