You might want to take a look at the ItemsPanel property:
Gets or sets the template that defines the panel that controls the layout of items.
Example:
<ItemsControl>
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<WrapPanel />
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
</ItemsControl>
And you can set it in a Style as follows:
<Style TargetType="ItemsControl">
<Setter Property="ItemsPanel">
<Setter.Value>
<ItemsPanelTemplate>
<WrapPanel />
</ItemsPanelTemplate>
</Setter.Value>
</Setter>
</Style>