You can move the location of the scrollbar using a ControlTemplate.
MSDN has an example to set the vertical bar on the left:
ScrollViewer ControlTemplate Example[
^]
To put the horizontal bar on the top, change its Grid.Row to 0 and adjust the row definitions so that the first row is auto. The ScrollContentPresenter goes in row 1.
<Style x:Key="LeftScrollViewer" TargetType="{x:Type ScrollViewer}">
<Setter Property="OverridesDefaultStyle" Value="True"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ScrollViewer}">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition/>
</Grid.RowDefinitions>
<ScrollContentPresenter Grid.Column="1" Grid.Row="1"/>
<ScrollBar Name="PART_VerticalScrollBar"
Value="{TemplateBinding VerticalOffset}"
Maximum="{TemplateBinding ScrollableHeight}"
ViewportSize="{TemplateBinding ViewportHeight}"
Visibility="{TemplateBinding ComputedVerticalScrollBarVisibility}"/>
<ScrollBar Name="PART_HorizontalScrollBar"
Orientation="Horizontal"
Grid.Column="1"
Value="{TemplateBinding HorizontalOffset}"
Maximum="{TemplateBinding ScrollableWidth}"
ViewportSize="{TemplateBinding ViewportWidth}"
Visibility="{TemplateBinding ComputedHorizontalScrollBarVisibility}"/>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>