This is demonstrated on a Conventional Website design; you will get strange effects if you try adding all three effects at once on a Supersite design.

The trick is any shape or group can have a filename set (e.g., filename=background).
One you have this, you can slap it onto your Pasteboards, using CSS3 Placeholders, on each of your pages in one of three ways: repeat-x, repeat-y and both.

In my example, I also made my original blobs invisible, with a fourth Placholder (CSS3 - hide Blobs).

CSS3 - Repeating Backgrounds.web

Acorn