How should I add wine to the sauce for my duck?
Your question makes me think of demi-glace. From your question, I would say that you're trying to get a nice shiny thick sauce for your duck, one that tastes of red wine.

If that's your goal, I would recommend you 


Reduce your stock down until it's about the total volume of liquid that you're going to want. The stock reduction should be roughly the consistency you want your final sauce to be.
Add an equal volume of wine
Reduce down to desired consistency (so about by half). 


This will give you a lovely sauce, with lots of that sticky goodness that reduced stocks deliver so nicely.

You might do this with all of your stock, then freeze cubes of unused sauce for later; they make a great addition to other bases. 

Left-over alcohol is not going to be an issue here, by the way, you'll have long since boiled/simmered it off.