Currently, when I define a custom style, it does not become part of the Visio program itself, but rather part of the drawing file in which I defined the style.

Instead of saving the drawing as a Visio template or manually copying custom styles from one visio file to another, can Quick Parts be made available (currently in Microsoft Word) where I can save the custom style I created to a Quick Part gallery so it's always reusable in Visio, regardless of the file I have open.