Yes.
Get a 20mm spanner or socket, take off the aircap and deflate the forks take off the top cap for the airspring and get 2.5mm of oil in there, I used fox float fluid which I'm sure is fine.
Put the cap back on and pump them up. You might not need to do this if you are lighter than me. I'm a big fella so I wanted them to ramp up a bit.
They are really sensitive to air pressures by the way a few PSI does make a lot of difference. They are very linear so they will use all of their travel fast if they are under pressured I have mine at the low end of the recommended pressure but the oil tweak keeps them from bottoming out.
There is a detailed video on this here, http://www.magura.com/en/products/suspension-forks-2010/prod/durin-marathon-8/info/movies.html