Brian - If you are building that from Method, you'd be using Actions.
I would suggest making a template using Assign Value to Action result, and then using Character Functions to replace text in portions of the template with action values.
For example:
1. Create an action result using Assign Value To Action Result, like <ExtraInfo><WebServicePassword>EnterPassword</WebServicePassword><WebServiceKey>EnterKey</WebServiceKey></ExtraInfo>
2. Have a Character Function that replaces EnterPassword with the real password.
3. Have a Character Function that replaces EnterKey with the real key.
That's just an example. But that should give you an idea.
Paul