How to handle off-topic questions during an interview

While offering an answer to another question on this site (this one if you're interested), I was reminded of a particularly challenging experience that occurred during my interview process that might generalize to others.

I went to a decently well-known and respected undergraduate university, and while I was interviewing for a PhD position at various schools, at least one of my interviewers usually asked me how I could help his son/daughter/nephew, etc. get into my undergraduate university. This was not at the end of the interview when all other questions (both his and mine) were answered, but rather it was at the very beginning of the interview (e.g. "Oh, I see you went to university X. My [insert familial relationship] is applying there this year/next year. How can s/he get in?")

Not knowing if I was in a position to decline to comment, I gave some brief, generic suggestions and then tried to steer the interview back to my own application and admissions.

I can see this possibly happening in many scenarios, from graduate admissions (like my own experience) to possibly postdoc or faculty job interviews. Has anyone else faced this sort of situation before (off-topic questions that while not "illegal" are somewhat uncomfortable to answer), and any suggestions on how to diplomatically handle it?