Very simple. Just leave the lens hood permanently in the forward position. The barrel problem is caused by a bushing (or two) getting deformed. This bushing is like a plastic wheel that slides along a diagonal slot when you zoom in and out. When you reverse the hood, with camera attached and leave the entire setup facing down in a bag or on a surface, the entire inner barrel will be bearing the weight of the entire setup. over time, it will stress the bushing too much and will cause it to be deformed causing the stiffness. Once it deforms enough or breaks, the lens barrel will also move at a different angle, causing it to rub or get stuck against the outer barrel (since the clearance is less than 1mm). The bushing is part of the inner barrel assembly. Once disassembled, without the proper equipment and expertise, it is almost impossible to to be assembled with the same precise optical tuning it once had. IIRC, only a few service centers in the world has the equipment to perform this calibration, and SG service center apparently does not have it. IIRC El Segundo NSC in California USA has it, thus is able to perform the repair. But I heard it is not cheap as well, if the lens is out of warranty.
Since the hood is mounted on the outer barrel, leaving it permanently on facing forward, will protect the inner barrel from sustaining any weight, saving your bushing from the extra load and stress. One thing I noticed is that the 24-70 with the hood permanently attached is the same length as the 70-200 with hood reversed. So when I swap lenses, I simply leave the 24-70 in the bag slot that the 70-200 vacated. Perfect fit.
BTW, Canon 24-70 mk1 also suffers from the same issue if you do not already know. Lensrental did a write-up on this a while back, complete with pictures and detailed explanation... but somehow it got deleted after a short while....
That is exactly what I do as well. Avoid resting the lens on the internal barrier, which means do not place it front element down, if done so the thin plastic of the bushing is taking the weight of all the glass, for a while its fine, but if this is the way the lens is stored most of the time, the problem may come after a few years.