Do you allow anyone else to login, register, sign up or comment on this website? If you are the only person who logs into the site then you can either protect your custom login page with either an IP address based security method or the simple query string method shown in the link below.
http://forum.ait-pro.com/forums/topic/protect-login-page-from-brute-force-login-attacks/
Nope, we have never looked at this before and have never been contacted about this before, but yes I agree it would be a very nice NEW feature to add to BPS. Thanks for the idea. :)