Comment 5 for bug 601723

Looking at the wikipage where you are trying this from
quote "Note2: Instead of using 'workaround', an alternative is to modify the file /etc/mtab by erasing the line that specifies the partition where the cdrom is mounted. This way the kernel thinks thats the /cdrom is not mounted and will not show the advice when installing ubuntu. I think this procedure is less dangerous than the one in the previus note. "
Can you try this and let me know if you are sucessful.