double fermentation?

I have been thinking and reading on double fermentation.  Wanted something new to try and have fun with.  I have a very good honey porter and would like to play with it more.  I was thinking about adding cherries and chocolate something kinda goofy.  So after the first fermentation would there be enough fermentables from smashed cherries (self smashing for more fun to start fermenting again.  Would I have to secondary the beer? And could I use the yeast left over (which should be a yes. I already do that with a second batch) For the chocolate I have read that would should secondary that and not ferment that because of the FAT you get from chocolate.  Which can interfere and make off flavors from the yeast.   

Sounds to me like a good way to add an infection to your brew.  I have one gallon cider jugs for that purpose. They usually end in an infection. Wait. They all have. But it was still fun!

one way to sanitize your fruit or zest from fruits or juices from fruits is to freeze them for a while.  I know when you freeze zest the spores pop and release acid. and we know that acid from lets say lemons cleans things or cooks things aka sanitizing your zest.  so my theory would be to smash cherries and put them in the freezer for a while then drop them in the beer.  Just a thought. 

I can't remember if I used Campden tablets or not. They work when I make fruit wine. (Five gallons of blackberry goodness is looking good)
As for whether or not to do this in secondary, I would say definitely. It might be a good idea to pitch some more yeast. You'll want to overwhelm any hitchhikers. Maybe a different strain just for fun. And then into a tertiary to separate the beer from the fruit. Fruit doesn't settle well by the way.
Do you have any one gallon jugs to play with? It would be a shame to lose an entire batch.