Adding a chocolate to a Porter

So I just moved a porter into the secondary and after tasting a cherry/chocolate ale from a local microbrew tonight, I am interested in adding a slightly sweet chocolate "undertone" to my porter.

My initial thought is to boil a cup of cocoa powder and two cups of Lactose (this is a 5 gal batch) in 16 Oz of water, cool and add to the secondary...

I await thoughts from those who have been there before me...

I wanted a LOT of chocolate flavor in my Chocolate Stout and used 1.5 cups of Ghiradhelli sweet cocoa with 10 minutes left in the boil. It worked very well, and the beer has a very strong chocolate flavor. Adding a little bit of vanilla helped too, it really brought out the chocolate flavor. It sort of... sweetened it up a bit. I really recommend the cocoa and some lactose, just be careful not to use too much. If you want the chocolate to be merely an aftertaste maybe don't use 1 1/2 cups. Good luck!
-Ben