Filter in a BCS

Hi!

I'm doing an External Content type in Visual Studio and I'm trying to create a default filter to minimize the amount of data that I get from the webservice.

I want to select all rows from the webservice between two dates.

Can I somehow create that filter with variables? Like filter from [today] to [today+3]??

In the .ect file I can find the filter descriptors but the Comparator is "Equals" I want them to be "bigger than" and "smaller than" ... but I cand find any documentation of it?

<FilterDescriptor Name="StartDateTimeFilter" DefaultDisplayName="StartDateTimeFilter" Type="Comparison" FilterField="StartDateTime">
                  <Properties>
                    <Property Name="Comparator" Type="System.String">Equals</Property>
                  </Properties>
                </FilterDescriptor>
                <FilterDescriptor Name="StopDateTimeFilter" DefaultDisplayName="StopDateTimeFilter" Type="Comparison" FilterField="StopDateTime">
                  <Properties>
                    <Property Name="Comparator" Type="System.String">Equals</Property>
                  </Properties>
                </FilterDescriptor>