I need a good sollution with good reasoning, so I'll try and give you as much information as I can.
So this guy does not use his brain. For instance: we put him on supp and he played soraka. He got caught and used redemption + ult + everything to save himself and had nothing left for the teamfight. So that got me thinking put him on a tank top where as less brain is needed as possible.
Then I read something about putting him on adc with a good supp, then at least bot lane wont be lost and then we have our best top/mid/jung playing their pref roles.
Currently we have him on supp, but these soraka like episodes happen with every supp he plays every game.
He is not a bad player... his farming aint bad and his reflexes aint bad either (his microgame is relatively good), only his brain, disision making is bad (he gets caught out a lot, we are all 4 in one lane, someone calls back, 3/4 makes it back to our own fountain, except him.
So thats all I can think off now, please ask me if you need more info and my question is, which lane should we put him and which comb/tactic should we follow so that there is the least damage done by him?