Edited by poster: Too longwinded. Same info and links provided.
Been trying to do this for a while, and the problem was finding an app that would not only overburn by a couple of minutes, but would also do it without putting gaps between the tracks.
Decided to join the .wav tracks of each disk together with this free app I found Mediajoin, which assures a seamless, no pauses playback, and then set Sonic to overburn by 5000 sectors, which was enough for the extra time needed to get disks 1 & 2 onto one disk.
Worked a treat, "The Wall" on one cd.
Another free app I found that would join the tracks seamlessly, and quickly, was Audiojoiner.