i wouldn't do that though, cuz if you decide to change your binding later, or if for example, you change your binding, it might not fit anymore. first measure yourself w/o the binding, then measure yourself wearing it, and see if there is a big difference. if there isn't that much of a giant difference in the chest area, then just go with the binding measurements. if it's a giant leap (more than 5in) then i say, put 1.5 inches more to the binding measurements. and that should do somewhat of a trick to the chest area. either way, you can easily wear it comfortably.
i only say this, cuz even when i tell them my chest measurements, they always leave a few inches just in case my boogage needs breathing space XD and when you are in binding, you want plenty of room to expand a little to breathe.