Implement Gridview Search Using LinqDataSource

I have two tables:

Orders
OrderProducts - An order can have 1 to many orderProducts records associated with it.

What I am trying to do (unsuccessfully) is to implement a GridView search using a LinqDataSource wherein the search returns Order results where any of the OrderProduct.Manufacturer columns contain a search query. I was hoping the following would work, however it seems lambda expressions do not work within a Where clause of a LinqDataSource (in VB):

<asp:LinqDataSource ID="dsOrders" runat="server" ContextTypeName="myDataContext" TableName="orders"
Where="orderProducts.Any(Function(op) op.Manufacturer.Contains(@searchTerm))">
<WhereParameters>
<asp:ControlParameter Name="searchTerm" ControlID="txtSearchTerm" DefaultValue="" />
</WhereParameters>
</asp:LinqDataSource>

In C# it would look like:

<asp:LinqDataSource ID="dsOrders" runat="server" ContextTypeName="myDataContext" TableName="orders"
Where="orderProducts.Any(op => op.Manufacturer.Contains(@searchTerm))">
<WhereParameters>
<asp:ControlParameter Name="searchTerm" ControlID="txtSearchTerm" DefaultValue="" />
</WhereParameters>
</asp:LinqDataSource>

The error I am getting is:

No property or field 'op' exists in type 'orderProduct' Any clues as to how to get this working within the LinqDataSource definition, or will I have to handle and set up a custom OnSelecting event?