There is no way to turn off the auto rotate (that I know of) for only one app, unless you have the code for the app. When they create them they decide if the rotation is allowed. Hence why some won't ever rotate even if you have auto rotate turned on.
The only option you would have is to turn off auto rotate for the whole device. Either by turning it off and leaving it that way, which will mess with the other apps, or turning it off when using that one app, and then turning it back on.