I haven't tried this yet, but
tltrude told me this will work. (or at least this is what i understood from it).
Make the window just like you would any other breakable window. Insteaed of using a broken window texture on the broken window brush, use the same texture as the unbroken window. Then, cut up this brush into pieces and delete some chunks, so that all you have left is some shards around the frame (or whatever looks best). Then select all the pieces that make up the broken window and make them all a script_object all with the same targetname (matching the target in the corresponding func_window brush)
Basically its the same as doing a regular breakable window except instead of having a single brush for the script_object (broken element), you use a number of brushes, leaving out the peices you want to be broken away.
I hope this works for you, because I am planning to use this technique on my map. Please post and let me know if it works.
