You can place pivot and pivot items in a grid, and once you have populated all pivot items, place a progress bar in the outer grid, it should encompass all pivot pages. Not sure why you would want to do that but it can be done.
Eg:
<Grid x:Name="LayoutRoot" Background="Transparent">
<Grid.Resources>
<loc:VisibilityToBooleanConverter x:Key="VisibilityToBooleanConverter"/>
<loc:InvVisibilityToBooleanConverter x:Key="InvVisibilityToBooleanConverter"/>
</Grid.Resources>
<!--Pivot Control-->
<controls: Pivot Name="Pivot1" Title="1">
<!--Pivot item one-->
<controls: PivotItem Header="1">
<Grid>
</Grid>
</controls: PivotItem>
<!--Pivot item two-->
<controls: PivotItem Header="2">
<Grid>
</Grid>
</controls: PivotItem>
<controls: PivotItem Header="3">
<Grid>
</Grid>
</controls: PivotItem>
</controls: Pivot>
<toolkit: PerformanceProgressBar IsIndeterminate="{Binding Visibility, ElementName=somecontrol, Converter={StaticResource VisibilityToBooleanConverter}}" Height="20" />
</Grid>