I am not a high elo player. I am a silver jank support main. But I believe that Jayce has high potential as a support. He has hard engage and an AOE slow on his hammer form q, and hefty peel on his hammer form e. In addition, his other form allows him to poke from a massive range with massive damage. I fail to see a single ability of his that does not synergize with the support role, excluding MAYBE his hammer w, but even that gives him some pushing power if you are the last champion alive defending your base.

start game. press p. buy sickle. press r. walk to lane. press q. after level 2, press e-q. You are not a fighter, not a duelist. YOU ARE AN AD POKE MAGE. If necessary, you can always look for easy picks by e-q-w-r-q-w-exhaust if you have it-walk in front of them-e. this combo is nearly unescapable if you have exhaust, and does heavy damage to boot. As Jayce support, you should be thinking as though you are a Nautilus. Look for the lost support who has wandered into lane without their adc. You thrive by pushing the enemy support and adc apart when you engage. Otherwise, you should just stay in mercury cannon and poke until you have to fight for dragons. Always remember to manage your mana. Keep about 150 mana on you at all times incase the enemy jungler ganks. this way you can always r-q-e and the gank if effectively null and void. Also attempt to proc omnistone as often as possible, but never sacrifice more than 100 hp for a proc.

Do standard Jayce things. If you do not know what those things are, then I highly suggest you learn Jayce in the top lane before you attempt to use him as a support.

No, I am not claiming that Jayce support is the best build in the game. But I am claiming that it is very viable. I do not support doing this in ranked unless you are confident on both jayce and the mechanics of the support role. My final note is to have fun. Part of what makes jayce support viable is that he can do anything you need him to, he's the swiss army knife of champions, you can build almost anything and take almost any runes if you know what you're doing.