In order to do it correctly you would need to make a metal mold of the origional and that use a plastic injector to form the part that is going to be burned out. The proble comes in the casting of it. Jeweler investment is fickle when it is poured and the plastic can become slightly torqued when you remove the air bubbles from the investment mixture.
I have actually made a 14kt gold case by molding the case with rubber and then injecting it with wax. Slight torque occured as well as having a lot of finishing to do. My dad wears the watch today. It was done from a Ricoh Watch. Had to modify the back because this watch had a snap on back that would not be able to be produced in gold. I took the snap on case from the origional and used it for the back.
I am a jeweler by trade, now I sell Jewelers tools, Beads, Findings ( Clasps etc). At one time we Manufactured all the Nautical Jewelery for Zales in Florida. This was before they decalared Bankruptcy and were bought out by Peoples Jewelers. Cost me a mint because they only paid 10 cents on the dollar owed.
Birdman