I see what you mean, but I still think there are issues....
If adding the powder before 'melting' (i.e. when it's still beads), you would have to melt it with a hair drier. In water, the powder would just settle out to the bottom of the bowl! As for mixing it in when you've got it melted, well, this depends entirely on how malleable it is - too stiff and it'll just be too difficult knead it and spread the powder evenly - you may end up with a speckled effect.
I've decided I'll get some this weekend and I'll try various things to see what it's really like. I'll even try your metallic powder idea.