You can just burn them to multiple DVD's. When reinstalling from the dvd's the installer will stop at some point when it fails at finding the bin files (the ones you had to put on the second DVD). When it does it's just a matter of putting the other DVD with the .bin file the installer is asking for in the optical drive and the install will resume from there. Basically the same process you use with any multiple CD/DVD install.

As an alternative, before re-installing you can just copy the content of the 2 DVD's into a folder on your PC and install from there. After the games is installed simply delete that folder with the install files fom your PC.

Or maybe consider a 1 or 2 TB's HD for backup purposes of all your games, an all around much better solution for backups (assuming you backup all your games and not just TW2).