As you know, Linuxmint is based on Ubuntu. So I thought, it might be possible to take Ubuntu as a base and turn it to Linuxmint with available Linuxmint software. Thats what I did.
I used Ubuntu Karmic Koala and turned it into Linuxmint Helena. You might use other Ubuntu base and turn it to respective Linuxmint distro, but you may need to follow different (yet similar) steps. Here is how I did it.