1. You can implement your very own custom filtering control and you will have total freedom over everything.
2. If you decide to stick with our stock FilteringControl, you can implement a custom ColumnFilterDescriptor inheriting from our stock ColumnFilterDescriptor. Since you don't want the grid to do any filtering at all, your custom ColumnFilterDescriptor can return a Expression.Contstant(true, typeof(bool))
LINQ expression, meaning that all records pass the filter. Since your custom ColumnFilterDescriptor is inheriting from our stock one, you will be able to read the data that the user has entered by examining base.* properties. Based on this data, you can perfrom any kind of "outside" filtering.
I have attached two sample projects that utilize a custom ColumnFilterDescriptor. While they are not meant for your case exactly, you can examine and debug them in order to tailor them for your specific requirement.
the Telerik team