The installation actually seems fairly straightforward, following the
instructions in the FAQ. Your only problem seems to be the 50GB free space on the drive where the user's folder is located. I would try the following:
1. On a disk where you have enough free space, create a folder, lets, call it "Folder".
2. Open a terminal and find the folder (I think it should be in "/Volumes/<diskname>").
3. Create a link from the user's home directory with the command "ln -sf /Volumes/<diskname>/Folder /Users/<username>/Library/Preferences/
com.nationalgeographic.products.cng120.68B1C
C4249876152EBE333BD4B7514ADB4D94062.1/"
4. Try following the instructions for the HD install.
That's the best I can suggest without the application to...