Grouping, filtering Id (int) columns as Name (string)

[Yaroslav]

Hello.
I have column:

<DataTemplate x:Key="CompanyNameDataTemlate">
            <StackPanel Orientation="Horizontal">
                <Button Click="CompanyNameButtonClick"  Margin="0,0,6,0" HorizontalAlignment="Center" VerticalAlignment="Center"  Background="Transparent"         BorderBrush="Transparent"         BorderThickness="0"  Padding="-4">
                    <Button.Content>
                        <Image Source="/ProMan;component/Images/Icons/Information16.png" Stretch="Fill"/>
                    </Button.Content>
                </Button>
                <TextBlock Text="{Binding CompanyName}"/>
            </StackPanel>
        </DataTemplate>

<telerik:GridViewDataColumn Header="EndUser" DataMemberBinding="{Binding CustomerId}" IsReadOnly="True"
                    UniqueName="EndUser" CellTemplate="{StaticResource CompanyNameDataTemlate}"
                    CellStyle="{StaticResource ReadOnlyCellStyle}"/>

It is everything ok, when simple displaing.
But when I want to filter records, or group them, I see CustomerIds (look at attached screenshot). The same situation if I have combobox column (binding by Id and showing Name) or GridViewDataColumn with Converter.
Is it possible to show Names instead Ids?

Also, is it possible to add button where is red dot on screenshot (button is needed for Collapse/Expand all action)?

[Yaroslav]

Sorry for UP.
Could you please give any advices for tasks described above?