One thing that I have neglected, although it seems readaliy apparent, is that adding dry sugar or malt extract will increase the level of alcohol of the beer. It would be easy to assume that adding a few ounces of sugar will not effect the alcohol level much considering pounds of grain were used in making the initial wort.
However a few ounces of priming sugar could be considered significant.
My fear was that dissolving the sugar in additional water would water down the beer. My wife, however, prefers to drink not more than 4% ABV. With this in mind, the target for my last brew was 3.5% ABV and about 3 volumes of CO2. The OG and FG were right on the money (a light 1.030 and dry 1.003 respectively) leaving the ABV at 3.6%. Tasty Brew indicates that 3.3oz of sugar should be added for this 3 gallon batch. 3.3 oz of sugar in 3 gallons of beer has a specific gravity of 1.003. That's 10% of the initial 1.030. The resulting ABV by adding this sugar is 4.0%!
So either assume that the priming sugar will increase the ABV by a 0.5%, or add water when priming.
To maintain the ABV of the beer the sugar should be in a solution equal to that of the original gravity of the wort. Knowing that white sugar adds 46 gravity points per pound per gallon, and a little algebra the equation can be worked out.
(oz of sugar) / (original gravity in gravity points) * 46 = cups of water
For a starting gravity of 1.030 add 1 and 1/2 cups of water for every ounce of sugar.
For a starting gravity of 1.040 add 1 and 1/8 cups of water for every ounce of sugar.
For a starting gravity of 1.050 add 1 cup of water for every ounce of sugar.
For a starting gravity of 1.060 add 3/4 of a cup of water for every ounce of sugar.
(3.3) / (30) * 46 = 5.06
For the 1.030 original gravity batch that I made the 3.3oz of sugar should be dissolved in five cups of water.
If you want to skip the math, just dissolve the priming sugar in about a quart of water for a five gallon batch.