Hi,
This is very good question, and my current understanding is that no, this is not possible at the moment. I hope that Support will correct me if I am wrong here.
The possibly good news is that TC9.2 introduced two new events for web service testing, one of which is the OnWebServiceRequest. Within the event handler for this event you should be able to create the Header part of the request with the proper Security node and add it to the outgoing request.
The only problem here is that I did not found yet how to generate a signature for the given part of the request (body, user name/password hash, etc.) using certificate by the means of .Net or native Win API.
