Unlike most of meta folks, I take duplicated questions as a disaster. Disaster that ruins the site.
Disaster inspired by the very site rules. An Uroboros of some sort - a serpent eating its own tail.
So, I propose a game to fit the current rules. As getting reputation points considered feature critical - let them get these points, but for finding duplicates. If the OP consider linked question useful - they can tick some special button and reward a duplicate finder.
It can be abused, yes.
However, I believe that this site should be less afraid of its users. There are many frauds already, despite of all the limitations. So, better follow the famous Franklin's quip and give people Liberty instead of "Safety".
It will require some programming, yes.
I realize that chosen stack makes it hard to make improvements. If it was built using LAMP, I'd volunteered with writing the feature myself.
Yet I believe that such a feature is not that hard to implement even with MS stack.