How to call a Web Service Data Control with pre-populated search criteria

I'ld like to present you with the following challenge:

We have an interface between our ADF application to a back-end application (Siebel) via Middleware, based of Web Services.
Given the datamodel of Siebel, you can image the complexity of the Web Service.

When the Web Service is called, some input values must be supplied.
These values should not be entered by the end-user, but should be 'hidden' from the user and defined by the application (e.g. Calling Application) or defined by navigation (e.g. contact ID, customer ID etc)

All the instructions and posts we have found on integrating Web Services via Data Controls  basically describe the following:
 - Create a Data Control based on the Web Service
 - Create a JSF page
 - Drag one (or more) of the input parameters to the page (all that you need)
 - Drag the WebServiceMethodCall(Object) to the page as an ADF page 
 - Drag one (or more) of the response fields to the page

To illustrate the WebServiceMethodCall see this image:

When you run the page, the web service is called (without parameters) and the result is displayed on the page.
On the page, you can enter some search criteria, and press the button
Then the web service is called and the page displays the result.

Now the challenge is:
How do we pre-populate the search criteria, bases on some application scope value (application name) and some session scope value (contact id) and make sure that the first call to the web service is done with these values.

Any idea's are more then welcome.

Answer will be posted as soon as we have it...
The question is also posted on the OTN ADF / JDeveloper forum