I use a transparent plastic sheet as the frame for air intakes at the side panel and front grille. I cut the filter and affix it to the plastic frame using a double-sided tape.



Here's the front grille. I use the grille's bent metal as a hook to hold the frame of the filter. For the side panel filter, I cut the plastic sheet into a 120mm x 120mm square shape and cut 4 triangles inside it, creating an "X" in the middle. I had to make a frame to prevent the filter from touching the fan blades. I put double-sided tape on all side and the "X" to make sure it kept the filter in place.



I also place the filter at the bottom air intake and PSU air intake. Since the casing already have a mesh filter there, I did not make another frame. I cut the filter according to the size of the existing mesh filter, affix a small double-sided tape to keep it in place and put the dust filter in between the casing and the hard mesh filter. It fits rather nicely.  I did not use a lot of the filter for this modification. There are still a lot of spares and I intent to use them as replacement when the filters get dirty.

The results:

           
I have to say the results are quite spectacular. The dust filter dissipated the blue LED light from the front fan and creates a rather nice uniform glow. The filter doesn't impede the airflow so much. Placing my hand in front, I can still feel the air going quite strong into the casing. And the best thing is, the insides of my casing so far, are clean and dust free.