You can pass an object of a certain entity to your XML-to-domain mapping by setting the 'Parameter' property of the mapping to that entity. This parameter will be used as the "parent" of the top-level mapping element, allowing you to select an association from the parameter entity to the entity chosen for the top-level mapping element.
Using this feature, you can create an object in your microflow, pass this object to the XML-to-domain mapping, and afterwards retrieve the object that was created in the mapping by association.