Woot. That's too bad.

I sort of lost track... did you try using a different IDE cable? If that fails then in theory you probably should be able to put a drive on the same bus as the CD-ROM drive in a master-slave relationship. They'd run at the same speed as the built-in IDE on a Beige G3. (Either UDMA mode 0 or PIO mode 4, forget which.) I believe I've heard of that being done.