As it is stated by the official xsane documentation, I created a symbolic link by the following command (in my case the folders are a bit different):
ln -s /usr/bin/xsane /usr/lib/gimp/2.0/plug-ins/
The link is there. Executing the above command again results in the following error:
ln: failed to create symbolic link '/usr/lib/gimp/2.0/plug-ins/xsane': File exists
But I cannot access xsane as a GIMP-plugin, even after logging out and restarting GIMP by doing so.