Allow employers to fire their employees without giving a cause for the first few months, giving them time to evaluate them. Problem solved.
Regulations like that just entrench the biggest players because they can afford the legal headaches of firing. Great way to incentivize people to start companies elsewhere.
edit: Consider that most people would request considerable more than they earn here now if at-will employment would be the case, offsetting any "gains" you might consider. In Europe wages are considerably lower than the US.
The "legal headaches" are only a serious problem if your legal system is broken.