Weblog client that supports WordPress custom fields

Does anyone know if there’s a weblog client, ideally for Mac, that supports WordPress custom fields? I’ve tried popular editors such as Ecto and MarsEdit but I’ve not yet found a client that allows you to specify custom fields. I think custom fields are a killer feature of WordPress because you can store metadata separately from the post itself and do the kinds of cool tricks my Technotags plugin allows such as geotagging and adding reference links at the foot of posts.