I like Charles' lateral thinking with a style change to include a paragraph number. That looks like a really good way to approach the question.

If you wanted the number to replace the %% then I would replace those with a Seq field and then update the fields to see these increment. To do this:
1. Create a field by typing the following line, selecting it and pressing Ctrl-F9
Seq styRunningNo
2. Select that field and Cut it by pressing Ctrl-X
3. Open the Replace dialog and replace all with the following settings
Find %%
Replace ^c
4. Update all fields

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Andrew Lockton
Chrysalis Design, Melbourne Australia