My girlfriend tore her grill off her Lexus with my garage door opener a few months ago. I used ABS pipe cement and fiberglass window screen to rebuild the mounting posts. I was able to add quite a lot of material.

I also did it on my mom's Jeep when she smashed the plastic fender trim/flare.
I've done it to all sorts of things made of ABS plastic, which is basically any black plastic in any application.

All that is a long way of saying ABS pipe cement works. It contains MEK (methyl ethyl ketone) and will partly dissolve your existing grill in order to form a bond. The liquid also contains ABS plastic particles that will solidify into a glossy skin before drying.

You could use this to patch it, but you need to practice if you want it to turn out pretty.

Good luck!