I have created a custom template for columnlayout pagercontrol as below:

   <Style x:Key="CustomNestedPagerStyle1" TargetType="igPrim:PagerCellControl">
            <Setter Property="Background" Value="{StaticResource PagerAreaBackground}"/>
            <Setter Property="BorderBrush" Value="{StaticResource CellItemNormalBorderBrush}"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="igPrim:PagerCellControl">
                        <Grid Background="{TemplateBinding Background}">
                            <VisualStateManager.VisualStateGroups>
                                <VisualStateGroup x:Name="Orientation">
                                    <VisualState x:Name="Top">
                                        <Storyboard>
                                            <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetName="pagerStroke" Storyboard.TargetProperty="Visibility">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="Visible"/>
                                            </ObjectAnimationUsingKeyFrames>
                                            <ObjectAnimationUsingKeyFrames BeginTime="00:00:00" Duration="00:00:00.0010000" Storyboard.TargetName="pagerStroke" Storyboard.TargetProperty="VerticalAlignment">
                                                <DiscreteObjectKeyFrame KeyTime="00:00:00" Value="Bottom" />
                                            </ObjectAnimationUsingKeyFrames>
                                        </Storyboard>
                                    </VisualState>
                                    <VisualState x:Name="Bottom">
                                        <Storyboard >
                                            <ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetName="pagerStroke" Storyboard.TargetProperty="Visibility">
                                                <DiscreteObjectKeyFrame KeyTime="0" Value="Visible"/>
                                            </ObjectAnimationUsingKeyFrames>
                                        </Storyboard>
                                    </VisualState>
                                </VisualStateGroup>
                            </VisualStateManager.VisualStateGroups>
                            <Border x:Name="pagerStroke" Height="1" VerticalAlignment="Top" Background="{TemplateBinding BorderBrush}" Visibility="Collapsed"/>
                        
                                <TextBlock x:Name="RowCount" Grid.Column="0" Height="30" Margin="0,7,0,0"  HorizontalAlignment="Right" VerticalAlignment="Center" Text="{Binding ElementName=txtNestedFLCount,Path=Text}" />

                                <igPrim:PagerControl x:Name="PagerItemControl" Grid.Column="1" >
                                    <igBase:Commanding.Commands>
                                        <ig:XamGridPagingCommandSource EventName="FirstPage"  CommandType="FirstPage" >
                                        </ig:XamGridPagingCommandSource>
                                        <ig:XamGridPagingCommandSource EventName="LastPage"  CommandType="LastPage" >
                                        </ig:XamGridPagingCommandSource>
                                        <ig:XamGridPagingCommandSource EventName="PreviousPage"  CommandType="PreviousPage" >
                                        </ig:XamGridPagingCommandSource>
                                        <ig:XamGridPagingCommandSource EventName="NextPage"  CommandType="NextPage" >
                                        </ig:XamGridPagingCommandSource>
                                        <ig:XamGridPagingCommandSource EventName="GoToPage"  CommandType="GoToPage" >
                                        </ig:XamGridPagingCommandSource>
                                    </igBase:Commanding.Commands>
                                </igPrim:PagerControl>
                            </Grid>
                      </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>

Where "RowCount" textblock will show calculated value of rows from code behind.

But problem with this approach is that once the row is expanded ,it shows correct count on its pagercontrol but pager text on previously expanded rows also gets updated with this new value.