My A Dynamic Task Reward System for Workgroups idea was intended to solve this exact problem and does so more efficiently both from a cost-perspective and a speed of work-perspective.
It could be combined with an upper and lower bound to the dynamic scaling and final steward approval to achieve pretty much the same thing, but better.
From what I recall your hesitation was that it would be difficult to keep track of workers, that problem is shared both with this proposal and my idea and the same methods can be used to mitigate it.