I have thought of the above method and tried it but it does not work !!
When you insert an aptoncd iso it gets mounted, and following that you get a pop up window asking you if you want to start package manager. Something must be there
Update: Ok I sorted out the problem !!
You have to go stepwise
1. Open Synaptic first (not as you mentioned second, above)
2. Click on Settings->Repositories->Third-Party Software
3. Click on Add CD-ROM button. You will then be prompted to load the CD. Leave that dialog box as it is, don't click ok
4. Open a terminal and mount the iso using the -o loop option
For example in my case
sudo mount -o loop /windoze/e/VBox/amd64/UbuKuXu-8.10-small-64bit-aptoncd-20090105-CD1.iso /media/cdrom/
Where /windoze/e/VBox/amd64/UbuKuXu-8.10-small-64bit-aptoncd-20090105-CD1.iso
is the path to the ISO
and
/media/cdrom/
is the mount point
5. Now go back to synaptic and click OK. The AptOnCD repository will automatically be added and the iso will be unmounted. Click close.
6. Refresh the repositories by clicking the reload button.
7. Mark packages to install
8. Apply
9. Mount ISO again as described in step 4 and the install proceeds