Apologies for the delayed response (had some major hoovering to do!).
I've got no issue with the parsing. By 'get away with it', I mean that the answer is derogatory and, although I take Cerasus's point about the structure and the hint of &lit, as you point out, 'offence' in the clue applies specifically to 'troll', not to the whole answer. So I don't think the setter could argue that they've told us we should be looking for an offensive term. (Even if they have, why include it in an Observer crossword!? It's not the Sun.)