[NTG-context] Full-page Figure?

I want to have a float (illustration for fiction, with caption) that takes up just one page, irrespective of the size of the image in the figure. This can be done with a \startmakeup, but makeup pages do not float, as near as I can tell; they interrupt the text (leaving a partly blank page); and of course they will not include headers and footers. And a float with [page] will start the figure on a new page as desired, but if the image is too small, other text will end up on the page, which is not the desired result. I want to vertically (and horizontally) center the figure on the page, with no other content but glue, in the main text block. Headers and footers should appear as normal. Is there a simple way to accomplish this? Mike