ItemsControl (WrapPanel) Grouping should split GroupItems

I have a ItemsControl with a WrapPanel as ItemsHost and multiple Groupings. Got this going so far with the following Templates:

<GroupStyle.ContainerStyle>
   <Style TargetType="GroupItem">
      <Setter Property="Template">
         <Setter.Value>
            <ControlTemplate TargetType="GroupItem">
               <Grid>
                  <Grid.RowDefinitions>
                     <RowDefinition Height="Auto" />
                     <RowDefinition Height="*" />
                  </Grid.RowDefinitions>
                  <ContentPresenter Grid.Row="0" x:Name="PART_Header" Content="{TemplateBinding Content}" />
                  <ItemsPresenter Grid.Row="1" />
               </Grid>
            </ControlTemplate> 
         </Setter.Value>
      </Setter>
   </Style>
</GroupStyle.ContainerStyle>
<GroupStyle.Panel>
   <ItemsPanelTemplate>
      <WrapPanel IsItemsHost="True" Orientation="Vertical" />
   </ItemsPanelTemplate>
</GroupStyle.Panel>

Now I have the Problem that every Group does start a new Column why I want it to Continue right under the last GroupItem and Wrap in the Middle of the GroupItem instead of at the beginning.

It should look like the Windows 8 Apps overview (not the start page, if you go down to the overview)

Is that possible?