How can I send an XMLDoc-based message without a soapenv wrapper

I am working on a request to send a simple XML message to a third-party system. I have defined the message as nonrowset-based, and in the code responsible for creating and publishing the message, I am gathering the data, populating an XML doc (from the CreateXMLDoc built-in method, then manually creating nodes to comply with the format provided by the third party), creating the message with the built-in-CreateMessage method and then sending with %IntBroker.Publish. When reviewing the XML of the message through integration broker, it looks as requested, but the third part is telling me that they receive it wrapped