Dont lie. Do not put yourself on the same level as this guy you are trying to get rid of.

Take the honorable route, and just tell him flat out, you arent interested. If he presses, then let him have it, but try to leave it at that if possible.

In situations like this, lying is the worst possible route to go. Its best just to be honest, and walk away from the situation knowing that you were honest and didnt have to lie abou tit.