How to use optional parameters in Web service call without making them mandatory

Hi,

We are invoking a web service as data source in our report and we are using report parameters to be passed to the web service.

We want report parameters to stay as optional. But as we use parameters in the Web service as web method argument they become mandatory.

I have following questions:

1. Is it possible that the parameters stay optional while being passed to the Web service

2. OR, is it possible to wrap formula fields around parameters and pass those formula fields as argument to the web service method.

Thanks