As for needing a reason, you don't. Just ask them to block the seats next to you (chances are they will feed you some BS about the flight being rather full and not all passengers have checked in and blah blah blah we dont care about you....)

I have often checked in @international and changed my seat to be in the middle of a 1-1-1 (a seat either side of me) so that anyone being checked in would hopefully not be given one next to a WP!