Need To Create &&<Query&&> Statement Programmatically

I am creating a web application that uses a using a web service to get data for my reports. Since the webservice only accepts 1 parameter called "sql" (the sql select statement), I am using the report's query string to get the data.

Here is the data source and dataset info I am using:

DataSource
Name: WebService
Type: XML
Connection string: http://localhost/myWeb/myWebService.asmx
Credentials: No credentials

DataSet
Query tab:
Name: WebService
Data source: WebService
Command type: Text
Query String: <Query><SoapAction>......</SoapAction></Query>

Here is a sample of the <Query> string that I use when I first build the report:

------------------------------------------------------------------------------

<Query>
<SoapAction>http://tempuri.org/GetDataset</SoapAction>
<Method Namespace="http://tempuri.org/" Name="GetDataset">
<Parameters>
<Parameter Name="sql" Type="String">
<DefaultValue>Select * From Customers</DefaultValue>
</Parameter>

</Parameters>
</Method>

<ElementPath IgnoreNamespaces="true">GetDatasetResponse{}/GetDatasetResult{}/diffgram{}/NewDataSet{}/Results</ElementPath>
</Query>
------------------------------------------------------------------------------
When the user selects a report in the web application, they are prompted for information about the sql statement, and then I can rebuild the <Query> xml fragment, substituting the new sql statemet for the default one. for example, the statement "Select * From Reports" would be replaced with "Select * From Customers where LN = 'Smith'".

Then I want to attach that new <Query> statement to the report and run it. How can I set this information in the report? I can't find anything that talks about it, but there must be some way!

Thanks in advance for your help!