1) select your whole page layout, then choose Edit->Copy As->PDF
2) paste onto your wireflows page.
3) set a fill colour of white, a one pixel border of mid grey, and optionally a drop shadow
You might at this point be thinking “but Andy, now I’ve pasted it as a PDF item I can’t edit it if the design changes?!” but you’d be wrong. Double clicking the pasted PDFs lets you do a linkback edit. Fucking badass.