I don't think it's necessary to bring it up whatsoever. If anything, the word count allowance on my essays was better served talking about more recent and relevant work experience.
After attending numerous MBA fairs and info sessions, it was made abundantly clear that adcoms understand that people are VERY different from the person they were back when they were doing their undergrad. (There was a thread here talking about people's regrets, and it mostly talks about things that occurred during undergrad.) There is so much personal growth that happens between then, getting a job, and the decision to pursue an MBA. That is why MBA applications give you space to explain things like a low GPA--but I don't think you need to explain your actual school choice, be it highly ranked or not. (If you went to well-known institution, it is noted on your resume, which will speak for itself without expending precious word count.)
I too went to an known undergrad school. I made no apologies or explanations for it in my essays and was accepted into my top school of choice. Another school I applied to (for an MSc, not an MBA,) after receiving my application, actually had the Director of their MBA Program
call me to persuade me to change my application into an MBA one, and join their program instead.
It is
very possible to promote oneself as a desirable candidate even with an unfamiliar UG degree. My inclination is to focus on other areas of your life and experience in your application.