Using XNA's XML content importer, is it possible to read in an array of objects with different subtypes?

For instance, assume these are my class definitions:

public abstract class MyBaseClass
{
    public string MyBaseData;
}

public class MySubClass0 : MyBaseClass
{
    public int MySubData0;
}

public class MySubClass1 : MyBaseClass
{
    public bool MySubData1;
}

And this is my XML file:

<XnaContent>
    <Asset Type="MyBaseClass[]">
        <Item> <!-- I want this to be an instance of MySubClass0 -->
            <MyBaseData>alpha</MyBaseData>
            <MySubData0>314</MySubData0>
        </Item>
        <Item>  <!-- I want this to be an instance of MySubClass1 -->
            <MyBaseData>bravo</MyBaseData>
            <MySubData1>true</MySubData1>
        </Item>
    </Asset>
</XnaContent>

How do I specify that I want the first Item to be an instance of MySubclass0 and the second Item to be an instance of MySubclass1?