To promote collaboration over competition and reduce the burden on the reviewer --
-Pass the burden onto the competitor/collaborators to reference/group eachother's ideas into a "final submission" which is what the reviewer would be responsible to review. Criteria defined up front based on what the reviewer wants to / is willing to actually review.
-This would also be incentivized by increasing the total reward with the number of ideas collected and incorporated along the way (there could be a certain set minimum and/or maximum)
-Reward is shared among all contributors whose ideas are incorporated into the final winning submission
-Maybe separate rewards for the number of times your idea is picked up
-Combined analytical approach to reward ideas that likely contributed to final submission but weren't explicitly referenced
-Incorporating someone's idea could mean combining it with your own, changing it a bit, or even completely disagreeing with it if it still helped lead to a better idea
-You can build on any idea or group of ideas or groups of ideas up until the submission deadline
-You don't even need any of your own new ideas if your best value is connecting, combining, simplifying, explaining others or posing new challenges (emphasis on "that could only work if..." or "what would work better than?" over "that would never work")
Ideally the challenges and solutions are useful and democratic and accessible so that any unrewarded contributions will not have been wasted time or energy anyway. A bit of a shift in mindset in that you "want" your idea to be stolen, it's a good thing if it's stolen, and the goal is to share the ideas that will help yourself and others assuming they will be stolen. You contribute not just for the potential financial reward (that does help too!) but because you want your ideas (or something even better) to exist.