<p>Normally, the method of passing workflow parameters to the workflow happens in the call to RunWorkflow.  However, with the WorkflowServiceHost, there is no such method call involved.  You simply call the Open() method on the instance.  Any ideas?</p>

<p>Of course, the implication is that I add more parameters to the service contract, but these parameters are not relevant for the consumers of the service.  They are more like configuration values.  </p>

You could set up a OneWayToSource binding on the DatePicker.SelectedDate property which pushes the text value into the ObjectDataProvider MethodParameter.
Starts by creating the ObjectDataProvider:
```
```
<ObjectDataProvider ObjectType="{x:Type theObjectType}" 
                        MethodName="GetDataForDate"
                        x:Key="odp">
        <ObjectDataProvider.MethodParameters>
            <System:DateTime>2008-01-01</System:DateTime>  
        </ObjectDataProvider.MethodParameters>
    </ObjectDataProvider>
```
```
Then bind the SelectedDate property of the DatePicker to the ObjectDataProvider:
```
```
<dg:DatePicker x:Name="datePicker" >
    <dg:DatePicker.SelectedDate>
        <Binding Source="{StaticResource odp}"
                 Path="MethodParameters[0]"   
                     BindsDirectlyToSource="True" 
                     Mode="OneWayToSource"/>
    </dg:DatePicker.SelectedDate>
</dg:DatePicker>
```
```
And finally bind the ObjectDataProvider to your ObjectDataProvider:
```
```
<dg:DataGrid x:Name="dtgGrid"
             ItemsSource="{Binding Source={StaticResource odp}}"
             AutoGenerateColumns="False"/>
```
```