I could never do much on the back wheel but i eventually learnt after watching a mate try it. Make sure you use both your arms and legs because i didn't at first and couldn't get anywhere.
Also can you roll up things? If so this will help you to learn and i will explain how next..
Try to rock yourself forwards and then back onto the back wheel and lean so far back you are going to fall off and then when you roll up something and you lift your rear wheel up the object, apply that motion and you will hop backwards. Keep trying that and get used to it and try to hop a smaller distance back all the time until you are no longer moving back.
An example, but don't land on 2 wheels, land on one:
http://www.trashzen.com/animations/anbkhop1.php
This might not help but i had the same problem as you and i was told this and i could do it after i tried it.
I would definitely recommend new pads and a grind though, that will solve the slipping brake issue. If you are not comfortable grinding your rim yourself, ask someone you ride with as I'm sure they can do it or know someone who can.