I'm a R2 waitlister, still awaiting an update like a number of us on this forum.
In my opinion, it is wishful thinking to believe that Kellogg's adcom will be influenced by your acceptance to another school. I'd even go so far as to say that it is a mistake to even mention this fact because the only reason you would do so would be to put pressure on them to admit you - and I do not think the adcom will respond favorably to any attempts at being pressured. There is a long line of people who will gladly take your place. They are solely focused on picking the best candidates to round out the incoming class - and in doing so on their timetable. If you have to make a decision about another school before knowing your final status at Kellogg, that is tough for you, but the adcom really doesn't care. In addition, it really isn't a significant update for the adcom. It's significant to you the applicant, but for the adcom they're focused on your accomplishments (work promotions, extracurriculars, etc.) and what value you would bring to Kellogg.
Pramodpg's idea about casually raising it over the phone would probably be the best way to handle it if you're going to do so.
This is all my opinion/speculation, so take that for what it's worth.