You need to hold the mouse button down on start up not shift for it to eject on start up.
I have PMG5 too. If the mouse thing doesnt work (and there's no mechanical eject that I know of) what about grabbing the tray and pulling it out (slowly of course) while the drive is still in place? Not ideal but you would pretty much be doing the same thing once you took the drive out.
Thats what I would do and if the drive implodes and destroys half the universe just buy another drive. There dirt cheap.
EDIT: Forget everything I said. I forgot theres a mechanical pinhole eject hole on the front of the drive. So you would need to take the drive out. Hehe.