I got this one: http://www.ebay.de/itm/280794425758 almost two years ago, it just fits between the drive and the connector when using a modified drive hatch. The modification I made was simple, I removed the mounting brackets and the plastic edges around them from the inside of the hatch, replacing it with a bit of foam to keep the drive in position. Put the adapter on the drive, slide the drive into the bay as if it is a PATA-drive, push the hatch into place and fasten it using the special screw. Ready.

Performance is more than acceptable, the thing boots (Linux) in a few seconds (that is, a few seconds after BIOS has done its thing of course). In other words, those 3€ for the adapter (incl. shipping) were well spent...