Sure someone has already came up with this.
Some of the top case support legs on a Falcon I'm building are in pretty bad shap, so made some sleeves about 3/8 diameter about 1/2" long with an ID where they can be pressed over the post to keep them from opening the existing cracks when screws are tightened. Went slightly larger on screw size as well.
But I got to thinking if those sleeves were longer, you could raise the case to what ever height you need ( with in limits of structural integrity of the case).
Be easy enough to trim lengths of plastic to close the gap, and even leave space at the back to access a CF card, install a slim line DVD over the floppy, and raise the keyboard for space over the memory card, expansion bus and NVRAM ( yes, I know you guys can desolder and install a replacement, I'm thinking of piggy backing mine to avoid catastrophic event!), all without hacking the case up.
Ok, back to soldering....