Avoidance of margin regulation was not really a factor in what happened here. For exchange traded stocks in the US there are two margining schemes: Reg T and portfolio margin. Reg T is available to anybody and gets you 2x. PM is harder to get, but not that hard: IB will give PM to accounts with at least 100k. PM gets you 6.66x. I think swaps can be used to do better than PM, but Huang didn't need swaps to get 5x.