XSD Validation with XSLT

Hello,

I guess my question might seem somewhat strange. The context is, that I
need to bring in content into a CMS that will validate it againts XML
Schema files. Some of the XML files that I want to import might not
provide data where the datamodel of the CMS might require this.

My idea was to validate the input against a xsd *by means of XSLT*.
This would *not need to validate the whole structure but only test
whether elements with unique names have a value or not. I a required
field is found to be empty a predefined value should be inserted. (e.g.
a -1 for xs:integer or n/a for xs:string)

To give you an example of my structure:
XML:
----
<employee>
	<name>Tom</name>
	<id></id>				<-- is required
	<managedBy>Hans<managedBy>		<-- is required
	<manages>Frank</manages>
</employee>

XSD:
----
<xs:element name="employee">
		<xs:complexType>
			<xs:choice minOccurs="0" maxOccurs="1">
				<xs:element name="name"
type="xs:string"/>
				<xs:element name="id" type="xs:string"
minOccurs="1"/>
...


OUTPUT:
-------
<employee>
	<name>Tom</name>
	<id>n/a</id>				<-- is required
	<managedBy>Hans<managedBy>		<-- is required
	<manages>Frank</manages>
</employee>

Any help is very welcome.

Robert