As much as it sucks, and as hard as it will be, it looks gotten to the point that the troll needs to be ignored until they get bored. (something I've had to do a few times since 2006).

No reaction. This is quite hard in an FC sense, as everyone needs to do it, as long as the troll get any reaction they will keep going.

If you've ever seen the tos-breaking extension voidlist (not suggesting that it's used of course) what it does, is the level of ignoring you will need to implement. If you've not seen it, the reaction is completely as if the troll is not there, to the point you walk through them without seeing them.