I wonder whether you can achieve the result you want by using a text box. In your master page, add a text box to the body and in its properties add the "Draft" image. Now apply the master page to the topics and all should be as you require.
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My guess is that you will have an extremely difficult time accomplishing this using a Master Page. At least you will if you are expecting to do it by applying the page to existing topics.
I'd guess the easiest way to accomplish it would be to create the draft image and configure your CSS file to use that image as a centered background that doesn't scroll. Then associate the CSS with all topics.
Then just before you compile in earnest, edit or swap the CSS with the desired (or no) image.
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Thanks for your tip. Alas, I can't get that to produce the results I'm after.
I was wondering whether I would have to go the CSS route. Time to brush up my image skills. Thanks very much.
The CSS solution worked beautifully.