It's nearly impossible. A friend and I just tried it and we didn't see any way to complete this level with only one character, no matter if Zoya, Amadeus or Pontius.
This video shows a very, very advanced tactic. I wasn't able to do it myself.
He basically uses the gravity arrow to get one of the barrels from the left to the right by continuously shooting gravity arrows at it. He then levitates it upwards and uses the hook on it.
But the good question that kotekzot already asked: Why do you want to do that? The achievement you're talking about is
Trine Kaput For Good?
Complete each expansion level using only one character
Searock Castle is not an expansion level, so you don't need to solo it.