I tried shortcodes and even tables, but the problem remains that all the microdata classes, etc. gets wiped out by WP.
I have several sites on the same topic and for now I'm writing the microdata into a (gasp!) FrontPage site that's taking it perfectly. Whatever markup I put in place, stays in place. I really wanted to use microdata markup in the other WP sites, but it's just not working.
I've been keeping up with the progress of a few plugins (Recipes only for now) and that author had the same problem with the initial version of her plugin --she could get the data set-up fine, but she couldn't go back and edit it without re-doing the whole thing.
There are a few other plugins that are supposedly being written for what I'm looking to do, but to be honest, I really don't want to build a significant body of markup based on a plugin whose author may or may not keep their plugin compatible with future versions of WP.