These adapters looked pretty basic, so I went with one from Hong Kong on eBay (see here) for less than £3 delivered. Although it is not as neat as having one the right size for mounting on the drive tray, I'm happy with it. Mine is stuck on to the drive tray with some sticky back velcro (hook and loop) and a cable tie. Its definitely not going anywhere

dmesg on my Empeg shows:
(...)
hda: TOSHIBA MK4025GAS, ATA DISK drive
hdb: SanDisk SDCFB-256, ATA DISK drive
ide0 at 0x000-0x007,0x038 on irq 6
hda: TOSHIBA MK4025GAS, 38154MB w/0kB Cache, CHS=4864/255/63
hdb: SanDisk SDCFB-256, 245MB w/1kB Cache, CHS=980/16/32
(...)
Partition check:
hda: hda1 < hda5 hda6 > hda2 hda3 hda4
hdb: hdb1
(...)
attempt to access beyond end of device
03:44: rw=0, want=2, limit=0
dev 03:44 blksize=1024 blocknr=1 sector=2 size=1024 count=1

I think the last part (beyond end of device) is related, I'm not too sure.

Mark, I'm not sure whether you've had time to have another look at the Hijack code for your idea (here), but I'm ready to try it out whenever you are.