Most fruit has very little sugar in it, 10% by weight or so. Checking the gravity isn't necessary, nor is extra yeast. As an example, I have a bag of frozen blueberries. A serving is 140 grams. 17 grams of sugar or 12%. Two pounds of them would add less to the batch than your priming sugar.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk