I haven't used this plugin yet. I came across your post and the plugin when I was searching for a similar solution...I'm trying to find a free trial of the plugin to see if it has settings to retain or create these metadata fields.

Andi you could try this - an Avid certified DNxHD transcoding plugin to Sorenson Squeeze 8. http://shop.avid.com/store/product.do?product=307799591993888