Adding Brown Sugar to Secondary?

I'll be brewing a recipe tonight, an Imperial IPA, that calls for adding 2 lbs of brown sugar to the secondary. There is no explanation as to how this is done, and I'm wondering if I need to make any adjustments in how I brew tonight? The recipe calls for a 5 gallon boil, but my electric stove will only boil 3, so I'll just top off to 5 in the primary. Should I go a bit below that 5 gallon mark to make room for the brown sugar in the secondary? I'm sure there is a common practice here, I just don't know what it is!

If you have a volume of 5 gallons when you pour the wort into your primary, when you rack to the secondary, you'll have a little less than five gallons. No need to worry about making room for the sugar.