Forms Data Controls :: Programmatically Change ItemTemplate Eval Statements?

I have a GridView with an TemplateField:

<asp:GridView runat="server" ID="gvReport" ondatabinding="gvReport_DataBinding">
<Columns>
<asp:TemplateField >
<ItemTemplate>
<asp:Label runat="server" Text='<%#Eval("answers") %>' /> out of <asp:Label runat="server" Text='<%#Eval("questions") %>' />
</ItemTemplate>
</asp:TemplateField >
</Columns>
</asp:GridView>

What I'd like to do on gvReport_DataBinding is change the field the Evals point to, so I end up with something like:

<asp:Label runat="server" Text='<%#Eval("answers_foo") %>' /> out of <asp:Label runat="server" Text='<%#Eval("questions_foo") %>' />

I have gotten this far:

TemplateField tf = ((TemplateField)gvReport.Columns[0]);

But I'm not sure what I should be doing with tf. tf.SomeProperty.Replace("answers", "answers_foo")?

Or am I barking up the wrong airplane on this one?