Hmmmm....if the flakes are small enough, they should be dry-sprayable through any gun with a large enough nozzle, but then we might as well just spray metallics if we've got that kind of equipment.
I think the squeezy talc bottle might still give you blotches, as the bulk of the material will be in the initial 'puff' with the surrounding areas getting less.

If you can get the handcasting working on a horizontal panel, why not go for a two-tone? Or even a single tone, but with the flat surfaces 'metallized' - that might be a neat look?