Okay, so you create a mining pool. But instead of getting his share proportional to contributed computing power, each member gets a chunk depending on how early he joined in. That's about it. Like Bitcoin Randomizer, only for pooled mining. I guess the reward could be adjusted/weighted for contributed hashes/sec to prevent this from being too unfair, and to encourage good mining rigs to join, even later on. So what do you think? Sounds to me like something that should have already been done by now, but I couldn't find it anywhere.
If someone actually implements this, I will be more than satisfied with a 4% tip or something.
(that's a modest 4 percent of the pool's entire gain, but I guess that's up to you...