The corsairs dont have the holes under the sides to bolt the skirts up there....
You've answered your question
1. Get some plastic spacers (the type that expand when you screw the screw into).
2. Grab a drill and make the required holes in the right places (the plastic plug / spacer will expand to fill the hole).
3. Attach sideskirts.
4. If you really want (which is what I also did), was put a few dobs of sikaflex or the like, just in case
5. Pull skidz
You end up with something like this: