In the WCF binding configuration, use the useDefaultWebProxy property to force WCF to use the default Windows proxy (which can be set from the IE network configuration):
<bindings>
<basicHttpBinding>
<binding name="ESBWSSL" ...everything... useDefaultWebProxy="true">
Then, in code before using the connection, do the following:
WebProxy wproxy = new WebProxy("new proxy",true);
wproxy.Credentials = new NetworkCredential("user", "pass");
and with your webrequest object before making the call:
WebRequest.DefaultWebProxy = wproxy;
I have not tested the code, but I think this should work.