UWP: How to override Ctrl-X, Ctrl-V, etc. in a textbox - win-universal-app

Question

I have a text box in my app. In this app, I am creating my own Undo/Redo functionality because the text in my textbox represents something much larger in memory, and I need to track these textbox changes to be able to undo/redo the whole project properly.
As part of that, I need to capture -- and handle -- many common keyboard scenarios on my own. Yes, I know this is going to be painful.
My major hurdle at the moment is the fact that the textbox intercepts (and even hides) the "usual" keys like Ctrl+X, Ctrl+V, Ctrl+Z and Ctrl+Y. It does this so that it can implement its own undo-redo, but I don't need the built-in undo/redo stuff. I would like to completely disable these keys in my UWP app.
I know that you can do this in winforms, but UWP appears to be a different beast.
private async void MyTextBox_KeyDown(object sender, KeyRoutedEventArgs e)
{
var ctrl = Window.Current.CoreWindow.GetKeyState(VirtualKey.Control).HasFlag(CoreVirtualKeyStates.Down);
// Handle special keys!!
if (ctrl && e.Key == Windows.System.VirtualKey.F)
{
Find_Click(null, null);
e.Handled = true;
}
else if (ctrl && e.Key == Windows.System.VirtualKey.R)
{
Replace_Click(null, null);
e.Handled = true;
}
...
else if (ctrl && e.Key == Windows.System.VirtualKey.Z)
{
// THIS DOES NOT FIRE
Undo();
e.Handled = true;
}
else if (ctrl && e.Key == Windows.System.VirtualKey.Y)
{
// THIS DOES NOT FIRE
Redo();
e.Handled = true;
}
else if (ctrl && e.Key == Windows.System.VirtualKey.X)
{
// THIS DOES NOT FIRE
CaptureUndo("");
e.Handled = true;
}
else if (ctrl && e.Key == Windows.System.VirtualKey.V)
{
// THIS FIRES, BUT THE PASTE HAS ALREADY HAPPENED
// SO e.Handled IS USELESS
string s=GetClipboardText();
CaptureUndo(s);
e.Handled = true;
}
}
I would really appreciate a nudge in the right direction.