There's a recipe for an IIPA on the "Can You Brew It" podcasts called "The Dankness". It calculates at less than 55 IBUs, but the actual IBUs are probably much higher due to the heavy, and I mean, HEAVY, late additions and whirlpool additions. I think their bittering addition is only 15-25 IBUs.
I think Heady Topper also skips the traditional bittering addition and focuses entirely on 15-10-5-0-DH. That's speculation though.