I am not sure i understand your question but i will try to answer it anyway.
Why not add a keydown/keyup event on your Xaml window?
and then C# Code behind it.
private void Window_KeyUp(object sender, KeyEventArgs e)
{
switch(e.Key)
{
case Key.F1:
radioButton1.IsChecked = true;
break;
case Key.F2:
radioButton2.IsChecked = true;
break;
case Key.F3:
radioButton3.IsChecked = true;
break;
case Key.F4:
radioButton4.IsChecked = true;
break;
}
}