I just finished using a product similar to JB Weld to fix the crack in ours. It's PC-7, a two-part epoxy paste. I used it a few years ago, and when the car got smashed on the freeway, the crack in the center of the grill reappeared. Use a Dremel tool or small file to grind out the crack to a "V", blow it out with air, tape off where you don't want the glue, put the epoxy paste in the crack. When it starts to finally cure in a few hours, you can press it in further and do final shaping. Use Bondo or glazing to get the shape just right. Wet sand it to shape. and topcoat. You can do the repair with the grill in place if it's the front point where they all crack. Then you don't have to bump it around. If you don't have the paint that was originally used, then you have to take it out and mask off the black areas (a pain).
If you have the grill out, Do what CudaNut said and reinforce the joint underneath with some mesh or wire