Using WSD Consumer with X.509 Authentication

I am trying to make WS call to an externally hosted webservice end point which is secured with X.509 digital signing and WS-Security. The X.509 has password, and needs to be provided before I can use it.

Does anyone know how to specify the password to the X.509 private key for signing the message?
Here is what I have in my policy file.

IS errors out because it cannot read the key, because it needs to provide the password.

Thanks in advance!!