WPF Customized TabControl

I have to develop a customized tab control and decided to create it with WPF/XAML, because I planned to learn it anyway. It should look like this when it's finished:

I made good progress so far, but there are two issues left:

1. Only the first/last tab item should have a rounded upper-left/bottom-left corner. Is it possible to modify the style of these items, similar to the way I did with the selected tab item?

2. The selected tab item should not have a border on its right side. I tried to accomplish this with z-index and overlapping, but the results were rather disappointing. Is there any other way to do this?

XAML:

<Window x:Class="MyProject.TestWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="TestWindow" Height="350" Width="500" Margin="5" Background="LightGray">
<Window.Resources>
    <LinearGradientBrush x:Key="SelectedBorderBrush" StartPoint="0,0" EndPoint="1,0">
        <GradientBrush.GradientStops>
            <GradientStopCollection>
                <GradientStop Color="Gray" Offset="0.965"/>
                <GradientStop Color="WhiteSmoke" Offset="1.0"/>
            </GradientStopCollection>
        </GradientBrush.GradientStops>
    </LinearGradientBrush>
    <Style TargetType="{x:Type TabControl}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type TabControl}">
                    <DockPanel>
                        <Border
                            Panel.ZIndex="50"
                            Margin="0,100,-1,0" 
                            Background="#FFAAAAAA"
                            BorderBrush="Gray