Create NSAttributedString from RTF Text File in iOS 6

Question

I need to create an NSAttributedString from an .rtf text file, so that it maintains the text attributes. In iOS 7, I use this code:

NSError *error;
NSURL *stringURL = [[NSBundle mainBundle] URLForResource:@"Text" withExtension:@".rtf"];
NSAttributedString *myAttributedText = [[NSAttributedString alloc] initWithFileURL:stringURL options:nil documentAttributes:nil error:&error];

However, initWithFileURL:options:documentAttributes:error: is only available in iOS 7.0

What can I use for iOS 6?