I was looking for information and the best link I found was http://zebbakes.com/2011/06/21/how-to-uninstall-a-velux-black-out-blind/, which was both informative and amusing.
It says to take a flat-head screwdriver, wrap it in a cloth, and then insert it between blind and glass, then twist it in small increments until the blind pops out by brute force.
It is possible to break the glass by using this method.