You could simply get the popular chieftec rails that are so abundant and get a drive cage from them and rivet it in there.
The only downside would be to cut some finger holes in the front so you could actually use the spring part and make it usable.
Another option is to cutout little slots in your drive cage and bend them over. Then you could mount a piced of plastic with countersunk screws and mount them to the drives. The plastic piece should fit your bent over tabs and make a rail. Just insure you bend another tab for a backstop so you don't push them in too far. If you make it snug enough, they should stay in. If not, then drill and tap a hole in the cage for a thumbscrew that goes into a hole in the rail.
Sound cool, or no? Sounds like a lot of work, so I'd rather rob from the Cheiftecs and save some work.
Here's some pics that show the second idea that I'm stealing from Coolermaster...(this one is in backward trying not to confuse the theory. That square is the CM's retention method. It would normaly line up with that square block you see in the drive above it.)
and a blurry drive rail...sorry, in a hurry!