This is also pretty simply accomplished with LibreOffice, which has page styles that can be triggered from the use of paragraph styles. In other words you could put a special “Full Page Illustration” style on your image in Scrivener, and then import the compiled document into a template that would have that style use a page style that changes the margins, even the paper orientation and other details. A page style basically controls everything about the look of the document, which means we can make major layout changes from Scrivener merely by creating styles and setting up the usage of them down the chain.
I’ve written on using Scrivener with LibreOffice in a few places, but this post really summarises how well these two can fit together, and offers branching off points to more practical demonstrations of how to do things like the above.
This also, by the way, works exceptionally well with the Markdown approach to using Scrivener, for those inclined.