There's a set of aluminum clips that bridge cracks in that area but I suppose how well they work depends on how badly your dash is broken. Can't offhand remember who sells them but I believe I saw them posted here.. hopefully someone else will chime in.
I repaired one that had minor cracks using some plumber's strap glued onto the backside so that it wasn't visible from the front. Actually the whole defrost vent was cracked loose, so I used strips of mechanic's wire glued across those to reinforce them. This dash went into a rough-riding 3500HD wrecker and it held up great. Roughing up the surface first so the glue can bite, and using Devcon Plastic Welder 2-part glue (epoxy?) got the job done.
The strap works great as it's fairly strong metal but it's bendable, and has holes in it already, just bend up a few pieces and cut them to fit, and glue them around the backside of the holes in the dash.
Sorry I don't have better pics; you can't even see the plumber's strap - but you can see the black mechanic's wire and the small blobs of glue.
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Same dash once I color matched it for the truck it was going into..
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Richard