I don't know whether all cars are the same but on earlier Subaru Legacy's removing the roof bars was a total nightmare and involved fully removing the interior headling, logic dictates this would be a sensible entry point as the roof bars must be secured into something fairly solid (structural) not just stuck to the roof, they are rated to carry at least 75kgs at high speeds so the pressures must be high. My aluminium look bars on the Sport may actually just be a cosmetic cover on the basic black bars as they are a slightly bigger diameter and appear to move slightly at the front as if they just slide over. I don't think this is a job for the fainthearted and may not prove worthwile in terms of effort expended and results achieved.
