We have some naive heuristics to try to detect bot movements (low ping, not many queued moves, moves every turn, etc) in the works, some of which are already implemented to try to reduce the numbers of bots on the main ladders. It's a tiny bit tricky to do however, most of the methods are still just going through testing.
We're hoping that people consider the reason we're trying to limit their access to the main ladders and do the honourable thing of keeping the bots in the bot ladder. It's slightly harder than just changing the URL, which we hope will help dissuade individuals.
The point I was implicitly making is that setting up a new server for bots and declaring "no bots allowed" on the main servers is not quite enough.