Is it possible to configure ms Unity container from an XML document and NOT from a file?
Not sure about this, but you can configure it programmatically without .config so that you can have your own XML file, read the settings and programmatically customize your Unity container. It is a shame that this side is not covered in a large part of the documentation. There are many scenarios in which App.config is not available or suitable.
Edit:
By default, this is App.config or the Web.config file for your application. However, you can download configuration information from any other XML file format or from other sources.
See: http://msdn.microsoft.com/en-us/library/cc440941.aspx
Why don't you save the XMLDocument in a local file on your computer, and then load this XML file into a Unity container.
If there is no restriction in saving the XML document, I think this will work.