Ok, not a REAL chocolate wine but I thought I
would share the following:

I got some "Stevia" from the health food store.
Stevia now also comes in chocolate flavor.

Soooo, I thought, why not add some to a glass of
some of my not so great wine. To my surprise it
was quite good. You could definitely taste the
the "chocolate" flavor. I used two drops but I
think you could use only one and tell a big
difference. If you have some wine to experiment
with - or if you just like chocolate, you might
give it a try. It is probably definitely easier
than trying to make a chocolate wine from
scratch.