There's more than one way to span a date...

In theory you can put HTML code right into a custom date format declaration. Actually, this did not quite work for some reason... somewhere in class year the code just gave up and pled for mercy.

\<\d\i\v \c\l\a\s\s\="\m"\>M\<\/\d\i\v\>\<\d\i\v \c\l\a\s\s\="\d\y"\>d\<\/\d\i\v\>\<\d\i\v \c\l\a\s\s\="\y\r"\>Y\<\/\d\i\v\>

Borrowing basic code structure from
http://www.opensourcery.com/blog/dylan-tack/quick-custom-cck-date-formatter

And meeting the specific request of a comment there, in fact.

Submitted as a sub-module to http://drupal.org/project/cck_formatters

It is currently posted as a patch here: Provide date field formatted into three spanned elements (month, day, year) ready for CSS to make it into a nice date block

Maybe mention here, the Date/Calendar section of the Site Building Guide
http://drupal.org/node/262062 (have not yet)