Because the person will be ejecting and inserting DVD's it can be tricky.
If you have an external drive you can copy the slices to, it would be easy. Copy them into a directory and then cat them together to the destination or piped into dd.
If you don't have the space on another filesystem, you need to use a fifo pipe. One gotcha is that writing to a device (e.g. cat slice | dd of=/dev/sdc1) you don't have a filelength because there is no inode for a partition, hence no filelength.
Also, you can't simply cat each slice to the fifo file because when the file is ended on the DVD in the sending shell, the receiving shell will get an EOF and the fifo pipe will be closed.
I found out that you need to create one fifo pipe for each slice (or alternate two of them).
Look at post #5 in this LQ link. I tested out a way of doing it. The subject came up again.
I don't remember for certain whether I tested it on an actual device. I think I did on a loop device.
A multivolume tar backup would probably work better. Suppose that disc 4 of 12 was damaged. You could still restore from discs 1-3 and 5 on.
Another way of doing it is to save the slice name, the offset and length in a catalog text file. Then use dd to restore the image slice using the offset from the catalog file. You could even include the offset and block count in the filename instead and then get the count and offset information from the filename. See the manpage for dd. There are options for blocksize, count and skip.
ps. I'm not home right now so I couldn't retest my idea. The posts I linked to originally were about assembling tar slices from DVD.