The URL of a proxy service can be customized. It is explained at  http://achala11.blogspot.com/2012/07/wso2-esb-proxy-services-with-custom.html

Ok,  lets try to access the WSDL.

The WSDL of a custom service url can be accessed from the following workaround.

You can use "main" sequence to route ?wsdl requests to appropriate working WSDL urls.
With this configuration, you can fetch wsdl for proxy service via http://localhost:8280/CustomURL/Part1/Part2?wsdl

If you have multiple proxy services with custom uris, you have to add a <case> statement per proxy service with appropriate wsdl urls.

<proxy xmlns="http://ws.apache.org/ns/synapse" name="CustomerProxy" transports="https,http" statistics="disable" trace="disable" startOnLoad="true">
   <target>
      <outSequence>
         <send />
      </outSequence>
      <endpoint>
         <address uri="http://localhost:8280/services/Version" />
      </endpoint>
   </target>
   <publishWSDL uri="http://localhost:8280/services/Version?wsdl" />
   <parameter name="ServiceURI">/CustomURL/Part1/Part2</parameter>
</proxy> 

<sequence xmlns="http://ws.apache.org/ns/synapse" name="main">
   <in>
      <property name="REST_URL_POSTFIX" action="remove" scope="axis2" />
      <switch xmlns:ns="http://org.apache.synapse/xsd" xmlns:ns3="http://org.apache.synapse/xsd" source="get-property('To')">
         <case regex="/CustomURL/Part1/Part2\?wsdl">
            <send>
               <endpoint>
                  <address uri="http://localhost:8280/services/CustomerProxy?wsdl" format="get" />
               </endpoint>
            </send>
         </case>
      </switch>
   </in>
   <out>
      <send />
   </out>
</sequence>