We have a custom Theme with custom Layout Templates.

I want to create a Page Template that uses one of the custom Layout Templates.

When I go to a Page Template, and click "Configure Page", I only ever see the standard Layout Templates.

I looked all around, and found no setting where I could configure a Theme for the Page Template (which I assume would allow me to select Theme-specific Layout Templates.)

Is it possible to use a custom Layout Template with a Page Template?  If not, are there any alternatives?