That's some very clear thinking RS!!!!
The idea of absorbing the energy in the stinger is thinking "outside of the box".
That got me thinking about lightweight energy absorbers since the far aft stinger location has a long lever arm. Velcro might work well. You can imagine one sode of a velcro strip (maybe the hooks side) attached firmly and smoothly to the inside of the tube. The other side (loops side) would be "pleated" to it with little pleats so that each section can be released to allow more payout of the line. As each pleated section is torn free, it eats up a bit of energy. Eventually all the little "pleat bonds" are broken and the loops side would be fully extended. The aft end of that strip could be attached directly to the tail cap of the keel for a fully extended hard limit or it could be attached with a bungee for a soft limit.
The nice thing about velcro is that it's lightweight, commonly available, and cheap.
RS, you've got some creative thinking going on!!!