WPF style which puts character ellipsis on button contents without replacing the ContentPresenter with a TextBlock and thus losing the ability to support access keys.

CharacterEllipsisButtonStyle.xaml

<Style x:Key="CharacterEllipsisTextButtonStyle" TargetType="{x:Type Button}">
  <Setter Property="FocusVisualStyle">
      <Setter.Value>
          <Style>
              <Setter Property="Control.Template">
                  <Setter.Value>
                      <ControlTemplate>
                          <Rectangle Margin="2" SnapsToDevicePixels="True" Stroke="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}" StrokeThickness="1" StrokeDashArray="1 2"/>
                      </ControlTemplate>
                  </Setter.Value>
              </Setter>
          </Style>
      </Setter.Value>
  </Setter>
  <Setter Property="Background" Value="#FFDDDDDD"/>
  <Setter Property="BorderBrush" Value="#FF707070"/>
  <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
  <Setter Property="BorderThickness" Value="1"/>
  <Setter Property="HorizontalContentAlignment" Value="Center"/>
  <Setter Property="VerticalContentAlignment" Value="Center"/>
  <Setter Property="Padding" Value="1"/>
  <Setter Property="Template">
      <Setter.Value>
          <ControlTemplate TargetType="{x:Type Button}">
              <Border x:Name="border" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" SnapsToDevicePixels="True">
                  <ContentPresenter x:Name="contentPresenter" ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" ContentStringFormat="{TemplateBinding ContentStringFormat}" Focusable="False" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" RecognizesAccessKey="True" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" VerticalAlignment="{TemplateBinding VerticalContentAlignment}">
                      <ContentPresenter.Resources>
                          <Style TargetType="TextBlock">
                              <Setter Property="TextTrimming" Value="CharacterEllipsis"></Setter>    
                          </Style>
                      </ContentPresenter.Resources>
                  </ContentPresenter>
              </Border>
              <ControlTemplate.Triggers>
                  <Trigger Property="IsDefaulted" Value="True">
                      <Setter Property="BorderBrush" TargetName="border" Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}"/>
                  </Trigger>
                  <Trigger Property="IsMouseOver" Value="True">
                      <Setter Property="Background" TargetName="border" Value="#FFBEE6FD"/>
                      <Setter Property="BorderBrush" TargetName="border" Value="#FF3C7FB1"/>
                  </Trigger>
                  <Trigger Property="IsPressed" Value="True">
                      <Setter Property="Background" TargetName="border" Value="#FFC4E5F6"/>
                      <Setter Property="BorderBrush" TargetName="border" Value="#FF2C628B"/>
                  </Trigger>
                  <Trigger Property="ToggleButton.IsChecked" Value="True">
                      <Setter Property="Background" TargetName="border" Value="#FFBCDDEE"/>
                      <Setter Property="BorderBrush" TargetName="border" Value="#FF245A83"/>
                  </Trigger>
                  <Trigger Property="IsEnabled" Value="False">
                      <Setter Property="Background" TargetName="border" Value="#FFF4F4F4"/>
                      <Setter Property="BorderBrush" TargetName="border" Value="#FFADB2B5"/>
                      <Setter Property="TextElement.Foreground" TargetName="contentPresenter" Value="#FF838383"/>
                  </Trigger>
              </ControlTemplate.Triggers>
          </ControlTemplate>
      </Setter.Value>
  </Setter>
</Style>