Superscript and Subscript in WP7

Question

I'm trying to show "H2O" with the 2 in subscript in a PivotItem Header.

E.g.

<controls:PivotItem Header="H20">
</controls:PivotItem>

I'd also like to assign the same value from code behind to TextBlock.Text.

E.g.

textBlock1.Text = "H2O"; // 2 to appear as subscript.

Is this possible with the version of Silverlight used for WP7?