I always wondered this too. I don't see why there wouldn't be a way. There are PCMCIA card bays for 5.25" bays..

laptop sata drives are just PnP, IDE already has adapters, the cdrom and floppies have adapters, etc. Zip is probably using a proprietary connector for something ordinary on the inside. Like how the SCSI external Jaz is just a internal SCSI Jaz with a 50pin to Centronics adapter. (Which has been killing me since I've got uniserver's SCA drive.. I think I'm going to try that this week.)