Gradually pour in boiling water, whisking constantly.
Let mixture sit until cornmeal absorbs water, 5 to 10 minutes.
Stir in half the oil and a little more boiling water, a little at a time, until batter is pourable.
Fold in fruit.
Put a large skillet or griddle, preferably cast-iron or nonstick, over medium heat.
When a few drops of water dance on the surface, add a thin film of remaining oil.
Working in batches, spoon in batter, making any size cakes you like; they will be thinner than pancakes.
Cook until bubbles appear and burst on the tops, and the undersides are golden brown, 3 to 5 minutes; turn and cook on other side until golden, another 2 or 3 minutes.
Transfer to warm oven and continue with next batch, adding more oil to skillet if necessary.