FWIW, to bring this sad tale () to a close, I gave up trying to put the new ear pads on my old HD280pro's and ordered a pair of Beyer DT-770's.
I've replaced the earpads on 3 pairs of HD280s and agree it's frustrating. But I stuck with it and figured out how to get them on.
Maybe you'd be willing to sell me your pair of phones with no earpads for a discount.