As described in this previous answer (thanks Fernando!), the "installer" shell script which WANDisco provide is actually just installing a standard APT repository. Although they ask for your details before you can download the script, there seem to be no terms and conditions attached to using their repository without doing so.
The below should add the repository on 12.04 Precise (the repository doesn't contain a
Source directory, which the
add-apt-repository command assumes it will, so I have used a slightly different method).
sudo sh -c 'echo "# WANdisco Open Source Repo" >> /etc/apt/sources.list.d/WANdisco.list'
sudo sh -c 'echo "deb http://opensource.wandisco.com/ubuntu precise svn18" >> /etc/apt/sources.list.d/WANdisco.list'
wget -q http://opensource.wandisco.com/wandisco-debian.gpg -O- | sudo apt-key add -
sudo apt-get update
To confirm that the new subversion package has been detected, run:
apt-cache show subversion | grep '^Version:'
If the 1.8 package is listed, you should then be able to install as normal:
sudo apt-get install subversion