Variable Substitution

I am trying to use variable substitution for Target Directory in my receiver communication channel. When I enable the field in the target message mapping, the message is sent to the URL which is passed from the incoming message just fine. However, it is in the XML file and it can not be there. When I disable the field, I get the error:

Attempt to process file failed with com.sap.aii.adapter.file.configuration.DynamicConfigurationException: Error during variable substitution: com.sap.aii.adapter.file.varsubst.VariableDataSourceException: The following variable was not found in the message payload: vc_url.

We are using XI 3.0 REL SP14. Can someone please tell me how I can use the URL value from the inbound message to substitute in the Target directory without having to include it in the outbound XML message.

This my current target directory variable substitution:

payload:x10quote,1,x10salesitem,1,vc_url,1

<?xmlversion="1.0"encoding="ISO-8859-1"?>

http://www.w3.org/2001/XMLSchema"xmlns="http://com.igt.sbo.zquoteconf"targetNamespace="http://com.igt.sbo.zquoteconf">

<xsd:complexTypename="x10quote">

<xsd:annotation>

http://sap.com/xi/TextID">

6a1515e0cdd011dbb6ab000bcd0b8460

</xsd:appinfo>

</xsd:annotation>

<xsd:sequence>

<xsd:elementname="x10salesitem"maxOccurs="999999">

<xsd:annotation>

http://sap.com/xi/TextID">

52fe2400fb3011da8302c12dd4f48159

</xsd:appinfo>

</xsd:annotation>

<xsd:complexType>

<xsd:sequence>

<xsd:elementname="x10linenum"type="xsd:string">

<xsd:annotation>

http://sap.com/xi/TextID">

52fe2401fb3011da94edc12dd4f48159

</xsd:appinfo>

</xsd:annotation>

</xsd:element>

<xsd:elementname="ItemCode"type="xsd:string">

<xsd:annotation>

http://sap.com/xi/TextID">

52fe2402fb3011da8075c12dd4f48159

</xsd:appinfo>

</xsd:annotation>

</xsd:element>

<xsd:elementname="Type"type="xsd:string">

<xsd:annotation>

http://sap.com/xi/TextID">

52fe2403fb3011dab2f8c12dd4f48159

</xsd:appinfo>

</xsd:annotation>

</xsd:element>

<xsd:elementname="Serial"type="xsd:string"minOccurs="0">

<xsd:annotation>

http://sap.com/xi/TextID">

52fe2404fb3011daa907c12dd4f48159

</xsd:appinfo>

</xsd:annotation>

</xsd:element>

<xsd:elementname="Description"type="xsd:string">

<xsd:annotation>

http://sap.com/xi/TextID">

d54fdf10004011db8390de27d4f48159

</xsd:appinfo>

</xsd:annotation>

</xsd:element>

<xsd:elementname="quotation_number"type="xsd:string">

<xsd:annotation>

http://sap.com/xi/TextID">

3d5fb860fb3611da9a0dc12dd4f48159

</xsd:appinfo>

</xsd:annotation>

</xsd:element>

<xsd:elementname="vc_url"type="xsd:string">

<xsd:annotation>