[WPF] How to get access to an element outside a style?

Question

I have many buttons, all of them have the other Content (Polygons, Rectangles, Ellipses etc)

Each Content's Fill and Stroke property use DynamicResources:

<SolidColorBrush x:Key="ContentsBorderColorEnabled" Color="Red"/>
<SolidColorBrush x:Key="ContentsBackgroundColorEnabled" Color="White"/>

<SolidColorBrush x:Key="ContentsBorderColorDisabled" Color="Gray"/>
<SolidColorBrush x:Key="ContentsBackgroundColorDisabled" Color="Gray"/>

An example of the Content:

<Rectangle x:Key="StopRect" Stroke="{DynamicResource ContentsBorderColorEnabled}" Fill="{DynamicResource ContentsBackgroundColorEnabled}" Width="8" Height="8"/>

And now, by the Style below I change the apperance of my button:

<Style x:Key="SimpleStop1" TargetType="{x:Type Button}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type Button}">

                        <Grid Width="10" Height="10">
                            <ContentPresenter Content="{TemplateBinding Property = ContentControl.Content}" />
                        </Grid>

                        <ControlTemplate.Triggers>

                            <Trigger Property="IsMouseOver" Value="True">
                                <Setter Property="Control.Opacity" Value="0.5"/>
                            </Trigger>

                            <Trigger Property="IsPressed" Value="True">
                                <Setter Property="RenderTransform">
                                    <Setter.Value>
                                        <ScaleTransform ScaleX="0.9" ScaleY="0.9"/>
                                    </Setter.Value>
                                </Setter>
                            </Trigger>

                            <Trigger Property="IsEnabled" Value="False">
                                <Setter Property="Stroke" TargetName="StopRect" >
                                    <Setter.Value>
                                        <SolidColorBrush Color="{DynamicResource ContentsBorderColorDisabled}"/>
                                    </Setter.Value>
                                </Setter>
                            </Trigger>


                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>

The problem is, when the Button's IsEnabled property is set to False I need to change f.eg the Content's Stroke and Fill. But somehow I cannot acces to it. How to resolve this problem ?

<Trigger Property="IsEnabled" Value="False">
   <Setter Property="Stroke" TargetName="StopRect" >
      <Setter.Value>
         <SolidColorBrush Color="{DynamicResource ContentsBorderColorDisabled}"/>
      </Setter.Value>
   </Setter>
   <Setter Property="Fill" TargetName="StopRect" >
      <Setter.Value>
         <SolidColorBrush Color="{DynamicResource ContentsBackgroundColorDisabled}"/>
      </Setter.Value>
   </Setter>
</Trigger>