I am wanting to make a shimmery frosting for a cake...I am hoping to pipe the frosting onto the cake (I am imagining it to be pretty detailed), without having to go back over the detail w/ a paintbrush. I've looked up using luster dust, but read lots telling me not to add it to my buttercream. Can I add it to royal icing? Can I do something else to make the icing shimmery before piping it on? Thanks!