IIRC, those plastic pieces just hold the mylar sheet in place (there is a mylar sheet between the daughterboard and the drive sled) they do not actually lock the daughterboard in place, they are only there to keep the mylar sheet from falling away and possibly making way for shorts. If you dont have the mylar sheet, these clips will be useless. You can make the mylar sheet, just trace out the daughter board on any size sheet and cut the excess. the thicker the mylar the better.
EDIT: It has been a while since I have worked on these, possibly the 2 side clips hold it in place. I can't be positive at this moment.