Wait what? I don't think that has worked for me, or I did something wrong because when I use the ladder on top to cross the barrel I always thought I was trapped for good. Same goes when the dude knocks me down. (I thought I had to break everything until everything's clear in the main section without knocking the other dude down and then let myself get hit to reach the bottom lol)
I used to kind of do what you are talking about but I just retried it tonight and I knock the dude down right away, then I clear the main section and then go to the top level to the left, knock the pillar down that drops the ladder, climb up then go over an orange barrel, then destroy that gray wall that takes a few hits, then go off the screen, showing up on the other side where there is a ladder to go down, then go off the screen after that to get to the other side and do the same until I get to the very bottom.
At the bottom, where that thick ladder is, you can destroy the pillar to the right of it dropping the barrel, then climb up the regular ladder go right to where you are right on the thick ladder(it's on a pillar), destroy it, then climb down and you are at the bottom section with the last two rows of walls to smash.
Basically, to sum up, you don't have to get hit to drop down to the bottom part(you can though), you just do what I did at the very top and go all the way off the screen ending up on the opposite screen until you are near the bottom.
It's so hard to explain and while I actually got knocked down before on purpose by the second dude, you don't have to to get to the bottom rows.
However, you HAVE to get rid of the rows where you start by before going to the top and knocking the pillar down that drops the ladder.
That's why it pays to knock the dude down right away, you don't need him to get to the bottom section.
Are you going off the screen after climbing the ladder on the top left and going over the barrel???
You show up on the other side.
Still would love a sequel though.