I'm not sure if you are able the WSDL via the browser, but if you can, just copy + paste the wsdl to a txt file.
See this threads for more info on importing a WSDL on a local file, good luck!
It doesn't work! I think it's not possible
It's indeed the only workaround which works. Sadly enough it's not possible to do it in the modeller directly.
It would be a nice feature.
If you have the username and password, I think you can. I don't test it but try the following: http://user:password@yourWSDLurl