You mean one person playing 2 hands and therefore seeing 4 pocket cards?
There aren't many people who have the skill to profit from that I don't think - if you pay 2 entry fees out of 6, you have to be pretty confident one of them will hit the money every time..... and those that do have the skill to profit from it probably play at high limits, where they wouldn't get away with it (because their opponents would soon realise!!)
I've always thought as well - if I were to cheat - then I wouldn't chose Texas Hold'em - I'd choose something like Omaha where you get 5 private cards (
) - that way, with 2 players, you're seeing 10 cards - or 20% of the pack!!