If this is temporary use time between these times to really talk about your concerns. There is a great book about communication called "Mars and Venus Together Forever"
Find ways to communicate that lets him know that his behavior becomes very immature and how it can be downright frustrating. Especially reinforce the behavior towards his friend and how hurtful this could be - maybe he thinks it just harmful fun. I would be careful about doing this in front of his friends. If the lies aren't the end of the world, just find ways to communicate this too. Sometimes it just takes persistence. Even when you think he isn't listening, you may be planting a seed. He respects your opinion so just gradually have him face his own behavior