What can you do to stop people from feeding

nothing. you don't have control over other players. no amount of raging, all-chatting or whatever can help you. the best thing you can do is mute, play your best and hope that you can win anyways. keep your cool, play smart. that's all you can/should do!

Lead by example and go ham

be like "aw damn" when they die or something, or go "xD crap" to show that you feel bad for them. and then don't give up hope. and when someone gets an early kill, say "gj" or "nice!" or something.

keep your teamates from tilting if you want to win :D or at least try to alieviate it xD

If they are feeding on purpose, there is nothing you can do.

If they are losing and are on tilt, kind words + YOU, going to help them can do a lot to reverse the state of mind they are in. In solo queue making one team member feel valuable and helping them catch up is so much more important than a dragon or a outer turret.

you can leave your lane and help them even if they top and you bot but everyone only wants to look out for them self (why should i give up my lead to help some guy who cant win thier lane. Remember when the time comes it effects you to thats why you even care if he feeds)