I would say that PostXML would be the way to go, maybe PostText
If you look at the snippet when you bring it in, it should be fairly self-explanatory.
If you wonder about how to get the xml that you want to post.
You could 1. just hard code it var myXML = <xml here>
or 2. Perhaps pull it from a file in the file repository (you would be doing a LoadXML from the repository to get your payload)