Shame on me for not updating this. I've had a fairly detailed discussion with James Serdechy of Stefan Audioart. Apparently, the HD280s are not "really" user replacable, even though they show the diagrams on how to replace the cables in the manual. He spoke with Sennheiser and they told him that you can send the phones it to have the cable replaced -- the diagram was only intended for folks such as sound engineers if they want to replace the cable. The HD280s are supposedly marketed to studio-types.
The question is -- is Sennheiser telling the truth? I'm looking at the manual right now and it looks as if any cable replacement would require at least SOME soldering. There appears to be a proprietary connector. The connector, I suppose, could be cut from the stock cable and soldered to the replacement, but the easiest fit. Of course, you still have the Sennheiser connector running from the left to the right ear (same problem with cable replacement for the 590s, I guess).
I do own a Stefan Audioart Vision 1 cable, but I'm not sure if I want to sacrifice it, and possibly the 280s to do a swap.