Not quite intercourse, but guaranteed to have her legs trembling long after he’s done.
While she lies on her back, her partner sits between her legs and inserts the tip of his member into her vulva, which he pulls gently closed around it with his thumb and first finger. He rubs her outer lips until his secretion moistens her vulva and then enters her completely. This is an excellent method of using the penis as a dildo. Because it’s different from intercourse and so locally focused on the inside of her labia, including her clitoris.