Work really hard to develop Telekinesis or some spiritual power do something for him he can see or practice and see if you can effect one of his chakras in some way that he can definitely feel when talking about it. Both of these may take quite a lot of time to learn especially if your starting out but it is possible.
Read his natal chart to him using Azazel's astrology.
Astrology also takes time to learn btw too you have to understand the symbols for the signs and planets and memorize what some of the stuff means or understand the energies well enough to talk about it or you will constantly be going back and forth to his chart and the ToZ astrology thing likely losing his interest and attention span long before you convince him of anything.
You also could use your mind to read things about this person you couldn't know ever maybe even events in their life etc in great detail if your more open. This might be convincing. This also takes some time to learn.
So maybe not much right now unless you can do something here but in a couple years yeah you could do something if you work hard at learning it and practicing each day. If this even is that worth it.