Yeh that definitely sucks they’ve rigged it up in a way that’s unusual for this type of work and also forces you in to this situation. Redirecting is good and probably your best option, canny and sensitive people will notice you doing this and take it for the hint that it is but dense or uncaring people will probably carry on steering things in to places you don’t want to go. If you’re forced to eat with them then yes redirecting the conversation will work up to a point but it is a subtle skill to do so non-obviously. It’s hard to advise specifically what to say like a script, though I would say if you just totally ignore the question altogether and switch topic very bluntly it’s going to come across strange and prompt confusion and questioning. You’ll need to somehow maintain the initial thread of their topic as lip service and then turn off down an unrelated avenue fairly smoothly. It’s what politicians do professionally. Reading the other responses to your post I think they’ve got some really good ideas on how to deal with this if you really get forced in to conversing against your will. It’s a subtle art of contributing basically nothing and rephrasing their same question back to them. I think another commenter suggested something along the lines of “I don’t know much about that what about you?” and similarly bland and useless resonses. This is friendly enough not to piss anyone off and lame enough to be totally uninteresting which hopefully invites little follow up. If they continue on their original track, you can combine this with seguing to another topic.
I didn’t suggest this to you initially because it doesn’t sound like your natural style and I think advice is best if it allows the recipient to handle things mostly in their own way while helping to avoid pitfalls in doing so. I guess you’ll have to navigate this daily frustration in a way a little outside of your comfort zone by carefully appearing to engage whilst really not and hopefully they’ll find you so boring they don’t bother anymore. Hopefully you don’t mind this giving the impression that you’re a boring person to the remaining 50% of your peers that don’t bother you so much but sometimes it’s a necessary evil.