Well, taking in the same smoke again should in theory have the same effect as just keeping it in longer. I mean if it's the same smoke, what does it matter if it was in your lungs, in a baloon, then in your lungs again... as opposed to just staying in your lungs the whole time...

What I do is take a pretty fat hit, but not expand my lungs to 100%. After I hold it in for a while and I need to breathe, I just suck in some more air, and that will buy me another 10+ seconds. I'd imagine the smoke is pretty much done after that.