You can use the panel bond as a filler, like you can sand it and shave it, but takes awhile to setup
https://www.amazon.com/Evercoat-Fibr.../dp/B000P72GKK
No filler is suppose to be used thick...just for finishing....but if u must...what i posted will be what ur looking for
Anything with fiberglass strains and ive seen it with aluminum shavings in it... thats gonna be your best bet