I can only suggest trying to put a layer of fabric on the underside of the dash pad and using expanda-foam to fill it. You'll need to trim off the raised edges where it has shrunk with a really sharp knife, fill the area and plane it back with a blade, then give it a light sand to get the profile right. I found this adhesive backed PU leather patch on ebay that I think will do an amicable job of covering the dash with and I think one sheet might just be enough to do the job. I want to mess around with the stuff I bought to cover the exposed painted metal in my cab. When I get onto it, I'll post pics of the end result. I posted the link in the 'what did you do to your truck today' thread -

https://www.ebay.com/itm/Adhesive-PU...72.m2749.l2649

It appears to be decent quality and it was a good price