How deep are the grooves ? As per AB, why could you not turn that section of the barrel down until the grooves were removed - say it might be down to 12mm OD - and then sleave it back up with a bit of steel tube, bonded on with green loctite. Turn it down to match the rest of the barrel OD.

For sure you need a lathe, but it feels do-able if you wanted to retain the barrel length.