Bizunit - substeps - context and return stream

Hi.
If i overwrite the execute the execute method for execute (for a substep) i'll get a stream as result. 
How can i pass it for another substep or even to a step?  I didn't get anything from documentation. 

I create both a step (LargeFileTestStep) and a subStep (LargeFileTestSubStep).

var largeFileStep = new LargeFileTestStep(testCase.LargeFileTest, ref stopwatch)); 

var subStep = new LargeFileTestSubStep(new Context());
var subStep2 = new LargeFileTestSubStep(new Context());

largeFileStep.SubSteps.Add(subStep );
largeFileStep.SubSteps.Add(subStep2 );

 bizTest.ExecutionSteps.Add(largeFileStep);