The solution is staring you in the face: Look again at the Seldén file you posted. What do you think is the function of the 97mm pin on the top swivel? Hint: An old CD works just as well. That and a short length of bungee cord at the bow is all you need. There is no need to modify the mast at all. And the simpler the system is, the more reliable it is.
BTW there is a reason the Harken High load is expensive. Together with the Bartels furler it is the only one I know that furls under high load. All the cheaper ones require you to take the tension off before furling the Genoa. In condition where I need to reef the last thing I need is a complicated reefing exercise.
Visit the cruising conference coming April and see how others have done it.