This time in cookbook style:

• Get the current CD's multi-session info by
  

  cdrecord -msinfo

  • You got a pair of numbers representing the start and end blocks of the latest session. We'll need them for the next step.
• Use mkisofs along with the next flags to create the image:
  • -M /dev/cdrw: path of your cd/dvd writer device
  • -C start block,end block: use the pair of numbers you got above, but you must increase the start block by 1!
    i.e. if cdrecord -msinfo gives "11231,44323", you should use something like that:

    mkisofs -J -R -o /tmp/myimg.iso -M /dev/cdrw -C 11232,44323

    Why the +1? I'm not sure! Common docs don't mention it!

• Burn the new image with
  

  cdrecord -tao -multi /tmp/myimg.iso