Hi Duraid,
If I were to try this, I would use two-part epoxy clay. It is two part resin, but in clay form. You have about an hour to work with it after blending before it starts to cure. You may even want to find a good potter or ceramics artist in your area that can help you mold the piece to ‘exactly’ match your guitar using pottery tools. Once it is cured, you can paint it to match your guitar. I don’t know how it will hold up to the tension of the strings, but I think it’s worth a try.
