I dont have a video or anything on it, but I was in a game where nidalee was executing minions with relic shield while in human form, despite saying it only works with melee attacks. She was using her human form auto-attacks to execute them.
Are you sure the execute passive was working? You're right when you say the human form shouldn't proc the execution passive (Killing a unit under 200 HP (+100% AD)), but the other passives (Giving gold + healing) should work if she kills the minions by any means if I understand it correctly.
Last-hitting with relic shield procs it, it's just the execute part that doesn't work.
