well one thing that seemed to work better for me is that i entered really late at night or early in the morning (before 5 AM) on most of the times that i have won.
maybe there is less 'competition' at those times for the IW ones.
before winning t-shirt from subway, i played 50 different codes. that one is a tough one to win.
i never could win the dentyne IW one though. lol so no gum for me