Is there a way to prevent deliveries from a stream?

My customer would is getting ready to have several dozen new developers start using RTC.  They have all of their code imported into about 20 components.

They would like to have the new developers 'practice' for a week or so before making real changes to the code.  I told them that we could configure a stream (or another project) that could hold the 'practice' change sets and baselines - but - I recommended that they not do this because of the chances of having an accidental delivery from the 'practice' stream to the real stream later. 

Is there any way to guarantee that there's no chance of the 'practice' code getting delivered accidentally to the real code in the future?  If we delete the 'practice' stream, my understanding is that the change sets and baselines still exist in the component and could be accessed in the future. 

Can this be done? Or is there a better way that I haven't thought of?

Thanks in advance.