On Fri, Jul 11, 2003 at 03:58:01PM -0700, Simon Gerraty wrote:
  | Nope, none of them have any impact on the spaces b/w words.
  | They act on individual words rather than the expanded string as a
  | whole, perhaps a flag to :C and :S that indicated that the
  | substitution should be on the expanded string would do the trick.
  | Like :C/ /:/x or something?

That could work, given :C and :S already support optional modifiers.