This is something I wanted to make as well, so I did some research/googling and found two black bacon recipes:
The first one, an old american country recipe, mixed molasses into a dry cure to produce a 'friable' mixture and then buried the pork in it. Yes, it was that detailed....
The second (can't remember where I found this one), suggested coating the pork in treacle and then sprinkling your dry cure and black pepper over it.
I ended up with something close to the second one. I rubbed some dry cure in to a piece of belly as normal and then attempted to coat it in treacle. This proved to be more difficult than I expected since the water had already started to leach from the pork. A couple of minutes of swearing and getting stuck in with the fingers produced a coating of a salty treacle stuff. Sprinkled it with a bit of ground black pepper and cured as for normal bacon.
Had some for breakfast this morning: a beautiful dark brown colour with a black rind, a lovely sweet taste with just a hint of pepper and treacle after-taste (you have to 'look' for it though). Yum.
Sorry I can't be more specific on the quantities. I just put a teaspoon(ish) of treacle on a small (about 1lb) piece of belly, but quite a lot of it ended up on me so I have no idea how much treacle, or even cure, ended up on the bacon.
Give it a go - it is wonderfully messy to make (at least the way I did it) and tastes pretty good too