Ouch what a huge pain. Yes there are ways to assist. As to taking the pain completely away, doubtful. He needs to be very aware of his injury allowing it plenty of them to heal. Physical Therapy is very helpful once the knee is ready for it.
You can use analgesic and anti-inflammatory herbs, create a salve to rub on the knee, or even teas. Epsom salt soaks or even comfrey poultice.