@Daniele, on OpenEars 2.041, I am successfully using OpenEars outside the mainBundle:
self.accousticModel = [[NSBundle bundleForClass:self.class] pathForResource:@”MyAcousticModel” ofType:@”bundle”];
[sphinxController runRecognitionOnWavFileAtPath:self.wavFilePath usingLanguageModelAtPath:self.languageModelPath dictionaryAtPath:self.dictionaryPath acousticModelAtPath:self.accousticModel languageModelIsJSGF:YES];
But I had trouble with version 2.502, as there are more restrictions than before at using custom models.