I think no. Also, I don't see the point in turning it off. In this case, the protocol will not be able to connect without a nickname.
Try playing with the "React on login error" option in KeepStatus settings (you can set some delay (~2-5 min?) to wait until your last session timed out and the old nickname is released). But this will work only if Miranda considers this "nickname already in use" error as a login error (I don't know if it does).