Its already built into the law.
When the risk profile fucks up, the taxpayers pay a big chunk of the shortfall.
If the risk profile REALLY fucks up (8% or more off), the taxpayers pay almost all of the shortfall.
The worse the law goes, the more pain to the the taxpayers.
This was intentional. It does not let America "ignore" the shitty health care bill. Instead, it forces that debate the liberals have been hoping for in terms of "single payor."