I can almost guarantee that many big guys may be strong enough to muscle out a couple of decent-looking dragon flags, but it often comes at the expense of imposing a lot of pressure on their lower backs.
The best way to approach this is by simply moving some of the lower body mass closer to the fulcrum, thereby creating a friendlier force angle and cleaning up technique. You can do this by bending one knee to 90 degrees. It softens the blow this exercise places on the lumbar spine. Switch legs on each set.