Alan, normally, a hand is over after you draw cards. But when the double up feature is activated the hand is not over with yet even though you have drawn cards. Because you get to decide whether to gamble on the double or not. That allowed a way to change the denomination on the hand. The double up feature is never actually played.
In short, you hit 4 Aces playing $1 8/5 Bonus Poker (pays $400) but switch it up to $10 denom and it pays $4000. There is no doubling up going on, just switching denoms.
And those who were caught and prosecuted were so stupid in the way they did it that they deserved to be caught and prosecuted.