If someone wants to do custom back-to-back sessions on one CD, then you can do the following:
- Add 20+ minutes of soft, classical music between the sessions.
- Remove the "wake up" tracks at the end of each session. This saves time on the CD that is used up by the 20 minutes of classical music. You may want to keep it at the end of the final session.

Another option is to repeat the Sleep Learning track, but this depends on how much time is left on the CD.

I use an iPod, and I create playlists. The playlists can be as long as I want (hours). I stick with repeating the Sleep Learning track and remove the "wake up" track. I play one of the playlists when I go to sleep or when I'm on a plane.