// in firstVC
-prepareForSegue:sender:
{
  VC *destination = segue.destination;
  self.flow.setupFlowBlock(destination);
}

// in flow
typedef FlowBlock = ^void (VC *destination);
@property (copy, nonatomic) setupFlowBlock;

- (void)showSecondVC:(VM *)sender sender:(id)sender
{
  [currentVC performSegueWithIdentifier:@"secondVCSegueName" sender:sender]
  self.setupFlowBlock = ^(VC *destination) {
    destination.viewModeller = ({
      SecondVM *secondVM = [SecondVM new];
      secondVM.routing = sender.routing;
      secondVM.dataModel = sender.secondDataModel;
      self.currentVC = destination;
    });
  }
}