You could use tyrael or lazy raider. However, you would have to manually control the movements. If not you'll most likely be reported.
You cant 100% afk in flex indeed. But botting the rotation is more than perfect, I usually top the meters with my 555ish DK in the most oqueue Flexes I enter, using Tuanha Premium CC for DK
What this guy said, you can't AFK during Flex, at all, you'll get kicked and reported. But using a bot for rotation is more than okay.