I don't understand what PVS is in this context, but it seems any attempt to completely automate this would struggle with false positives.

There might be >350 polys visible from weird camera locations, but if the player is never there in normal gameplay you don't care about them. If they do end up in such a weird position in one game in a thousand (say a rocket jump lifts them up to somewhere normally inaccessible) it's not the end of the world anyway, the game will just render slower for a few frames.