I'm afraid that isn't possible.
There's no distinction between a hard link and a file itself.
Imagine the following: There's a file with NO NAME on the harddisk from byte 4 to 8.
You CALL the file FILE1.
So if you open FILE1, the OS looks the file up in a table and finds it should look at byte 4 to 8.
If you hardlink it (symbolic linking is different!), to FILE2, FILE2 points to byte 4 to 8.
So if you open FILE2, the OS looks the file up, and finds it should look at the same byte 4 to 8.
Conclusion is, if you burn it on CD, you burn the whole file instead of the link.
I guess the reason of the behaviour of du isn't the hardlinks, since hardlinks cannot be distincted from real files normally, but I'm not quite sure.
Are you sure the links are hard and not symbolic? It's possible to get symbolic links on a dvd.