If it's not important today, I agree with you. When it becomes important enough for you to do something about it, I promise to give you my undivided attention. I wish I had time to socialize with you, but right now there are people depending on me I have to get back to. Something to that effect to end the call.
You're missing his point. He ONLY said it wasn't important to him today. It might be tomorrow after he gives it some thought...or maybe next week. If you have found out his "why", then you would know that it is important to him, but maybe doesn't want to be rushed into it. At this point, you need to find out his "when".