If there is a higher demand for workers during certain hours, shouldn't the workers be paid higher for those hours? Seems like a fair trade off? If you want ala carte hours, you should pay ala carte prices. Only way I can think to do it though is by regulating time software... something like "if you use flexible hours, you must comply to these regulations" where in they specify custom pricing.
That only works if the supply of workers is limited. And in this case, the low-wage bracket, it isn't. It's absolutely flooded with people, so you can't expect the workers to command any such bargaining power. It's simply supply and demand, and there simply isn't enough demand to satisfy the huge supply of low-wage workers.
My solution: Company towns. Give the workers daycare, food, accommodation, training/education and pay them peanuts... in the middle of nowhere. But that'll never fly, because the argument really isn't about "fair-wage", it's more about "entitlement" so people see it as some sort of loss instead of a huge gain in a market that really isn't favoring them at the moment.