What I discovered was that in the year or so that has passed since the last time I used it, it had stopped working.
The problem turned out to be a libusb compatibility problem -- installing dev-libs/libusb-0.1.12-r7 did the trick, and the phone is now wiping itself quite satisfactorily.
It's a dead technology, and I have no more devices which need it, so I'm afraid that I won't be updating the ebuild any time soon. Still, I hope that this tiny post may have been of use to someone out there.
