If I understand the requirement correctly: you have deployed a SOAP virtual service, if some client sends a request for retrieving the wsdl information then you want to send that back.
In that case the SOAP virtual service will receive an HTTP request as follows: GET /<myUrl>?wsdl
A simple, pragmatic way to implement this is to add a transaction similar to the above in your vsi. You can see exactly in the inspection view of your virtual service what the signature of the incoming wsdl-request is. Add that signature to your vsi and put the wsdl info in the response.
Incoming request will be transformed by the HTTP Listen step into a request object as follows:
Operation : GET /<myUrl>
Argument(1) : wsdl
The SOAP DPH will find that the payload is NOT a SOAP:Envelope and will not transform the request object and hence the request will reach the Response Selection step with above signature
You only need to add a META response, no exact matches needed.
Hope this helps.
Cheers,
Danny