They're portable in the sense that you can carry them around. However in every other sense they are not portable. The cable is heavy, they are comparatively fragile when stacked up against the MDR-7506, DT250's and HD25's of this world, and most importantly, ZERO isolation in either direction.
And TheReaper... The first attempt was just using a knife and a 5-pronged precision shearing tool (AKA, um, my fingers) to prove my hypothesis. It was horrible but proved to me that it worked.
The first proper time was using an automated cutter. I programmed in a suitable cutting path and let the machine go. I was sort of hoping that the very high speed blades would cut through very quickly before the foam moved. However being optimised for cutting metals, using it for Grado pads made the pad fly off the cutting table with an interesting "zwirnnnn" sound, suitably shredded. In retrospect, not very clever.
Second and third attempts were made using a Dremel with a rotating cutting tool. It wasn't that even, but a lot better than seeing Grado pads ricocheting around the room.