This is an attempt to codify the best-guess algorithm suggested for ambigious name components on hcard-brainstorm. Processing is only attempted if the entered value is not a valid value for fn.
fn
Result:
<div class="fn"> <span class="n"> <span class="given-name">Hieronymus</span> <span class="additional-name">Karl</span> <span class="additional-name">Frederick</span> <span class="additional-name">Baron</span> <span class="additional-name">von</span> <span class="family-name">Munchausen</span> </span> </div>