Suppressing Panel Input on OpenFileDialog class

[Beorne]

I'm working on winCE 5.0 with .NET CF.
I'd like to suppress the automatic appearance of the input panel when
I open a new openFileDialog and the edit box automatically takes the
focus (I have an usb keyboard and I don't need the input panel).
My function is something like:
private void button_Click(object sender, EventArgs e)
{
if (openFileDialog.ShowDialog() != DialogResult.OK)
return;
// ....
}
I've seen that the right function (that I have wrapped with pinvoke)
is:
BOOL SHSipPreference ( HWND hwnd, SIPSTATE st );
but I can't use it on openFileDialog, I don't know how to extract the
dialog window handler in cf and I don't know where to put the
instruction.
Some help?
Thanks