well if they offer it on the spot, and it's better than what you have now, then why not? or, be honest and say that you don't think you'd be a good fit for that specific role, but you think that you'd still make a good fit for the company should something else come up. if they don't offer it to you on the spot, which most places won't, shortly after or shortly before the second interview say that you found other employment but ask if you can keep in touch. get their business cards. and yeah, any employee in an at-will position should always keep on top of their interviewing skills. always be one step ahead of your employer, you never know when they'll up and decide to close your division.