That was Ian's first option, which does not appear to be possible (not mentioned in the documentation, lack of relevant attributes on the ol and li items).
I had a brief attempt at working with Ian's second approach. I tried to add a hangingIndent element as part of the li element, then tweak the hangingIndent and initialIndent attributes to get the paragraph in the right place. This kind of succeeded for the HTML output, the the PDF output put the hangingIndent paragraph on the same line as the previous paragraph, and then seemed to indent the next item. In any case, it would be an evil and ugly hack that completely goes against the spirit of structured documents.
My suspicion is that there is no satisfactory way of doing what Ian wants.
bruce