Have you tried using your HD280Pros at work? They are closed back recording studio headphones, explicitly designed to not let a lot of sound out, so that backing track isn't picked up by vocal mic etc. So passive noise isolation should be O(20dB), which should be sufficient unless your workplace is very noisy.
I have a pair of AKG K271 mk2 at work (same category as your HD280), as well as the Bose QC35s. The AKGs give a bit less isolation, but for extended use (6-10h) wearing comfort as well as audio quality, they blow the Bose right out of the water. The QC35s have been relegated to travelling only.