Olli,
What about bringing another character and casting Create Portal as soon as you enter the prison? does that work it, or are you prevented from casting spells immediately?
Failing that, I'd try the athletic jump out of the dowel room. It can work...
Or perhaps getting a party in there, but letting the pixie-vampire-whatsis get killed off quickly? I don't think you get XP if you're dead...
Just a thought (or two).