Hi Ed,
When you create a layout, don't use a real image but the blank "[Template]" image that is always at the end of the thumbnails.
Treat that as a real image for size, borders, text etc. and then save as a Layout. You can have as many "template" images as you like on a page.
Use the template as you have said from Custom; you will then be able to drag & drop images onto the template
Terry.