I'm not sure it can be done in a .bat file - but IF it could, it would be a bad move. You would be storing your password in cleartext - ie it's indexable by any searchengines that is allowed (intentional or otherwise) to search your machine.

Myself, I run keyclone, hit the command, then I disable the DNP filter, type my password once(which is the same for all 5 accounts) and they all login at the same time. I prefer to keep my password as something I have to type.

Passwords are there for a reason. Accepting that is alot better than circumventing it.