I have a beer with molasses kegged right now. I only used a 12oz bottle in a 5-gallon batch, and it was still arguably too much. If you're going to do it, just know it might leave your beer with an odd, lingering, burnt sweetness.
Luckily, I made this a very big beer. 7.8% ABV. I have a SodaStream, and I tried adding carbonated water to a glass - about a 2:1 ratio, dropping the alcohol to 5.2%, and taming the Molasses with it, and it's actually delicious.
As weird as this sounds, I'm going to take my keg out of the fridge, add a gallon of distilled water, and drop two ounces of Centennial in a weighted bag for a day or two, then chill it back down. [EDIT - I'm also going to add a half teaspoon of gypsum to maintain mouth feel after dilution, and help accentuate those new hops] I'd rather have a weaker, more aromatic beer. Since I'm kegging, I can do that.
If you're bottling, you can't rightly "fix" an experiment afterward. So, if you are bottling, I recommend erring on the side of caution with molasses.