- (void)registerMethod:(NSString*)methodName withBlock:(void (^)(NSArray*))executionBlock {
    [[self XMLRPCMethods] setValue:executionBlock forKey:methodName];
}

- (void)executeMethod:(NSString*)methodName withArgument:(id)argument {
    [[self XMLRPCMethods] objectForKey:methodName];
    // HOW TO EXECUTE BLOCK WITH ARGUMENT???
}