With that in mind, drag this link to your bookmarks bar. The font, if it's installed on your system, should be picked up without issue, and so the only thing you'll need to specify is the location of the image iA Writer uses for its background. The image can be found here, inside the application package:
Once you have the image you need to put it somewhere where it can be referenced by CSS, and then replace
URL_OF_BG_IMAGE in the bookmarklet code with the path to the image. Alternatively--and this probably is the easiest method--you can convert the image into a data URI using this simple tool (hat tip Brett), and then replace
URL_OF_BG_IMAGE with the resulting string.