If you set to now and did it manually, would it be likely to be done by the time you got a better answer here? If the answer is "possibly", then I would just get on and do it manually. Either that, or think of a way of reorganising your data so that the cells in question are taken out of the range where the sum is taking place. You haven't said WHY you need those cells to be excluded or WHAT the purpose is. With more information, forum members may be able to offer a better solution.

You could also post a sample workbook here.