I drop my pieces on the cement patio in my back yard. That way you get no metal flakes from the hammer. Hold high over head.....SLAM!
You can't really direct the area of breakage tho.....but it sure helps take out frustrations....
Go to www.mediabaskets.com and look at their fish saver. They have one for your tank. I think he's closed down right now because he's moving but he creates a lot of stuff for nano's. Go to the aquapod category and you will see what you need.