Interviewing for a job I don't want, at a company I do

[Anonymous]

I interviewed for a position at company. The job posting was somewhat vague, but at the interview, I realized it's not a job I'm interested in. I would, however, possibly be interested in working for this company, but in a different, but closely related, department. By way of example, the two departments are similar in nature in the way that enterprise sales is very similar to commercial sales. The department I'm interviewing with and the department I'd rather be in report up to the same person.

I know that I'm a finalist for the position, and I have an interview with my potential boss's boss. I know that I don't want the position, but I'm wondering if I should do the interview in the hopes that I impress them so that if something comes up in the other department, they'll think of me. FWIW, I tend to do really well in interviews (I'm not trying to sound arrogant, but I know how to project that confident, professional air that employers are looking for and I'm pretty good at small talk to keep the conversation going).

So, two questions --

1. Should I continue interviewing?
2. If I got an offer, what's the best way to decline and not burn bridges?

[Anonymous]

Keep interviewing. If they make you an offer, you can decline and say while you appreciate it, you thought it over but you would rather do X than Y. If they really like you they may try to accomodate your request.

A few years ago I interviewed for a job that had 50% what I wanted to do and 50% something I wasn't interested in. Through negotiations they ended up splitting the position into two different jobs and I got to do the work I wanted 100%.