There isn't an obvious way to fix this without dramatically changing the way pages are rendered. The reason the link expires is probably that the garbage collector picks them up after a timeout interval. I remember this was something on the order of 10-30 min.
Honestly though, HN is a free service built with an experimental programming language buy a guy who worked full-time as a seed-stage investor. That's a miracle in itself. You're not going to "shame" anyone into fixing it.
[1] http://en.wikipedia.org/wiki/Closure_(computer_programming)