Or you could wait until the watter was choppy enough that oxygen gas and nitrogen gas from the air was more readily put into the water therefore decreasing the waters density and allowing for a higher bouyancy. Thus the boat could more easily support the added weight of a person 1 pound over its carrying capacity.

There may also be ways to decrease the weight of the fat person such as forced stimulation of smooth intestinal muscle to contract so internal epithelial tissue can force contents in his digestive system to be expelled, thus decreasing his weight.