I have been using the url intercept method to pass data from javascript to objective C by passing the data as url encoded parameters and using NSURLProtocol to intercept the
You should definitely use a POST. You just need to set up the request for it. You may need to make sure that the data is encoded and take care of a couple other details.:
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
[request setHTTPMethod:@"POST"];
[request setValue:myMimeType forHTTPHeaderField:@"Content-Type"];
[request setValue:[NSString stringWithFormat:@"%d", requestData.length]
forHTTPHeaderField:@"Content-Length"];
[request setHTTPBody:requestData];
[self.playerView loadRequest: request];
Alternatively, you can send a multi-part document or form values.