now i'm going to give you some tips, i can backwheel 36" and have bunny hopped to back the same. however wether i'm doing it right or not is a different matter haha.
i reckon you're better off starting pedal ups on something worth getting up. try 3-4 pallets
like 24". if you can pedal up onto things to two wheels you're half way there.
if you get the technique etc. it should just be a case of a bit more speeed ( not to much mind!) and a lot more effort, bigger kick etc. concentrate on pushing your arms and the handle bars away from you into the sky. push your whole body behind you're back wheel. look at pictures of benito and imitate that.
also, no pedal ups are done with ease, at all. benito can't just hop up onto stupidly high things without any effort/thought. it's impossible. it will become easier with practise. but the effort and power still has to be there.
here's me doing it
as I say whether I'm back wheeling "right" I don't know. good luck also, it will take time a good few hours atleast (of practise)