I guess I have too much cake information in my head. Last night, I dreamed that I was trying to make Banana Cream buttercream icing, using instant pudding. If you learn how to do this, let me know.
Anyway, on average, you would add about 3 oz of melted chocolate to your BC recipe.
Theresa 
You can take a pudding mix and dissolve it in the liquid from your bc recipe (milk or water) then continue mixing your bc as usual. If you already have bc made and you add the pudding mix to it, then your bc will be very grainy and won't have a nice texture when people eat it. I don't know about adding melted chocolate. Sorry I can't help there.
Thanks, but then I would not be able to use it, as I do not make American Buttercream for my cakes. I only use French Buttercream, which does not have added water or milk.
Theresa
Another forum for the same question?
http://www.cakecentral.com/cake-decorating-ftopict-56501-.html
http://www.cakecentral.com/cake-decorating-ftopict-56505-.html
Here's a frosting recipe which uses instant pudding mix:
http://www.recipezaar.com/178205
How to Thicken Frosting using instant pudding mix (if you've run out of powdered sugar)
http://www.kraftfoods.com/main.aspx?s=cookingschool&m=cookingschool/tipdisplay&tipid=4348&cache=N
How to make Chocolate frosting, using cooked pudding:
http://webfavorites4dumbbells.com/chocolate_pudding_frosting_recipe.txt
HTH
Please share your recipe
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