Freelancer ID might work, but Trader ID doesn't allow bombers as far as I am aware.
Most of those Trains with Zoner ID's are powertraders anyway, but I understand your point that a Liberty faction should stay away from Zoner ID's, what with all the non-Zoner idiots using them because they think it makes them immune to piracy.
Also, Freelancer ID's/tags are supposed to be incredibly hard to get, aren't they?