Did you try:
-(BOOL)shouldAutorotateToInterfaceOrientation

UIIn terfaceOrientation)interfaceOrientation {
// Return YES for supported orientations
return( interfaceOrientation == UIInterfaceOrientationLandscapeRight );
}
This has allowed me to have a landscape keyboard when in landscape mode.
However, I have not been able to figure out how to make the keyboard always show up in landscape only mode if the app is in landscape only mode.