Hi Theo,
CM SAF does provide the SID, i.e., the direct solar radiation through a horizontal plane at the Earth surface. As you know, DNI is defined slightly differently (the plane is following the sun), but there are probably ways to convert both quantities into each other.
See for example the instructions for the solaR R-package (http://solar.r-forge.r-project.org/), which deals with the solar radiation and photrovoltaic systems.
Kind regards,
Jörg