I would probably look through the threads people have posted so you can refine your idea even further, but I wanted to add a few personal opinions into the mix.
I think it's find if you use the runes to trigger your spells, as others have said it's nothing different from an arcanist doing it. However, you said that you are using the runes to tap into his power that he can't readily use on his own, so I don't think that it would make much sense if you were to 'buff' someone else with a rune and not have it an affect on neither their aether or your own. There has to be a price for gaining that power, be it from power from the runes (if you decide to go with powdered aether crystal  route) or bestowing your aether to that person for them to gain that power.
You could always make your runes be charges. Like your character puts what little aether he can manage on his own into the rune, having it slowly grow from it until it becomes charged, then when he needs the power, unleash the rune to use said power.
I think it's find if you use the runes to trigger your spells, as others have said it's nothing different from an arcanist doing it. However, you said that you are using the runes to tap into his power that he can't readily use on his own, so I don't think that it would make much sense if you were to 'buff' someone else with a rune and not have it an affect on neither their aether or your own. There has to be a price for gaining that power, be it from power from the runes (if you decide to go with powdered aether crystal  route) or bestowing your aether to that person for them to gain that power.
You could always make your runes be charges. Like your character puts what little aether he can manage on his own into the rune, having it slowly grow from it until it becomes charged, then when he needs the power, unleash the rune to use said power.
