I'm currently doing a dual hdd mod in my xbox and was considering doing the same thing.
After hacking the shit out of the existing trays, you start to think, "wouldn't it be easier to just fabricate my own". I would say just pick up some varying thicknesses of plexi and try to duplicate a simplified form of the hdd tray.
Seeing as my tray is for two drives i'm just going to screw them down from the bottom screw holes on the drive. That way all you really need for the main part of the tray is a flat piece of plexi. If your going to glue it together I recommed WeldBond Glue(can get it at home depot) it works well on plexie and dries perfectly clear.
Probably the hardest part of the whole procedure will be finding clear parts to replace the posts that the screw go through, I have yet to find anything myself. If I do find something suitable i'll let you know. But i suppose you could just cut out the original posts, clean them up and use those that might actually look pretty cool
Of course you would need a right sized drill bit to drill through the plexi, to fit the posts properly.
Just some ideas, good luck with your tray