USB SuperDrive Placement

Second that. The Superdrive is not sturdy enough to take the weight of an iMac. Put it off to the side or get a stand like a TwelveSouth Riser or a Backpack Shelf. You could probably even just place it on the foot of the iMac stand or velcro attach it to the back of the iMac.

I would not do that. You can get stands or risers that let you safely store things under the iMac, like:

Monitor Stand Riser, Klearlook Foldable, Height Adjustable Computer Stand

I am concerned that the material making up the the bottom of the SuperDrive enclosure is not sturdy enough for long-term weight bearing.