Contex-fill Around edges

How do you use Fill as follow. I need to add a few mm all round the edge of a graphic. Ie Printing a 'too the edge' A5 when the file is exactly A5. It must have a bleed all round first, and I need to fill the bleed, then trim back to A5.

 I have done it in the past using View context-fill but cannot deem to do it any more. Please help.