WebService in Grid FilterTemplate

[Kristijan]

Dear Experts,

I am using RadGrid to show my application data. In order to filter the related values I am using FilterTemplate with RadComboBox as it is nicely describe in this example. I Have up to 5 columns using this kind of tiltering.

Due to performance reasons I would like to change the server side loading of the filtering RadComboBoxes with the use of Web Services. 

<telerik:GridBoundColumn DataField="OwnerId" UniqueName="OwnerId" DataType="System.Int32" />
<telerik:GridBoundColumn DataField="OwnerName" SortExpression="OwnerName" DataType="System.String"
    UniqueName="OwnerName" AutoPostBackOnFilter="true" FilterDelay="800" ShowFilterIcon="false">
    <FilterTemplate>
        <telerik:RadComboBox ID="RadComboBoxOwners" EnableAutomaticLoadOnDemand="True" Filter="StartsWith"
            AllowCustomText="true" AppendDataBoundItems="true" runat="server" OnClientSelectedIndexChanged="OwnerChanged"
            ViewStateMode="Enabled">
            <Items>
                <telerik:RadComboBoxItem Text="All" Value="" Selected="true" />
            </Items>
            <WebServiceSettings Path="~/DesktopModules/VipCrm/Wsi.asmx" Method="GetUsersFilter" />
        </telerik:RadComboBox>
        <telerik:RadScriptBlock ID="RadScriptBlockOwners" runat="server">
            <script type="text/javascript">
                function OwnerChanged(sender, args) {
                    $find("<%# ((GridItem)Container).OwnerTableView.ClientID %>").filter("OwnerId", args.get_item().get_value(), "EqualTo");
                }
            </script>
        </telerik:RadScriptBlock>
    </FilterTemplate>
</telerik:GridBoundColumn>

When trying to implement this I encountered the following problems:

1. If the <Items> are present no WSI request triggers.
2. The RadComboBox loses its selected value though view state is enabled.

Has anyone tried this approach? Do you have suggestion to solve the above problems?

Regards,

Kristijan