derive from foreign xml schema

This is an xml example I want to be able to validate with my selfmade schema. The whole EncryptedData part is actually syntax of the XML Encryption specification.

<?xml version="1.0" encoding="UTF-8"?>
<Foo xmlns="http://www.foo.org/FOO">
    <EncryptedData>
        <EncryptionMethod
            Algorithm="http://ift.tt/1cxljQC" />
        <ds:KeyInfo xmlns:ds="http://ift.tt/uq6naF">
            <ds:KeyName>John Smith</ds:KeyName>
        </ds:KeyInfo>
        <CipherData>
            <CipherValue>DEADBEEF</CipherValue>
        </CipherData>
    </EncryptedData>
</Foo>

So I tried deriving from XML Encryption and came up with this:

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema
    xmlns:xsd="http://ift.tt/tphNwY"
    xmlns:xenc='http://ift.tt/rAMjm9'
    xmlns:xenc11="http://ift.tt/1uFgHSc"
    xmlns:foo="http://www.foo.org/Foo"
    targetNamespace="http://www.foo.org/Foo">
    <xsd:import namespace='http://ift.tt/rAMjm9' />
    <xsd:import namespace='http://ift.tt/1uFgHSc' />
    <xsd:element name="Foo">
        <xsd:complexType>
            <xsd:choice>
                <xsd:element name="myItem" minOccurs="1" maxOccurs="unbounded" type="anyType"/>
                <xsd:element ref="xenc:EncryptedData" minOccurs="1"
                    maxOccurs="unbounded" />
            </xsd:choice>
        </xsd:complexType>
    </xsd:element>
</xsd:schema>

But then my actual xml would have to look like this. I need to prefix all the XML Encryption elements with namespaces as I imported them.

<?xml version="1.0" encoding="UTF-8"?>
<foo
    xmlns="http://www.foo.org/Foo"
    xmlns:xenc='http://ift.tt/rAMjm9'/>
    <xenc:EncryptedData>
        <xenc:EncryptionMethod
            Algorithm="http://ift.tt/1cxljQC" />
        <ds:KeyInfo xmlns:ds="http://ift.tt/uq6naF">
            <ds:KeyName>John Smith</ds:KeyName>
        </ds:KeyInfo>
        <xenc:CipherData>
            <xenc:CipherValue>DEADBEEF</xenc:CipherValue>
        </xenc:CipherData>
    </xenc:EncryptedData>
</foo>

But I also fail to actually change the import into an include as target namespaces differ. (my own being different from the one defined in the xml encryption schema) Is there a way to do this so you can even use it without the namespaces? Or will it only work with prefixes?