Help Needed? WPF Style Triggers

Question

I have a class A derived from DependencyObject.
Class A contains a dependency properties "X".
Class B derives from Control and has a dependency property "PartA" to hold Class A.

In XAML I can't use triggers for properties of Class A.

<Style.Triggers>
        <Trigger Property="PartA.X" Value="0">

             <Setter Property="MyProp" Value="90"/>

         </Trigger>
 </Style.Triggers>

The above is not possible.Is there any possible way?