My reply there, please go there for further discussion and their rebuttal:
How much is the bounty?
Will it pay out if I just tell you how it can be done?
It is pretty simple actually. Bribe some nodes by sharing some of the double-spend theft.
There is created an incentive to aggregate mining power in order to sell capacity to double-spend. It is an economics issue. Just because it can't be accomplished on the controlled testnet is irrelevant.