There seem to be certain time slots where you win every time. I'm not sure if it's as simple as X number of minutes for winners, Y number of minutes for losers or if they do something like 5,000 winners per day is equal to 200 per hour, so if they haven't have that many people play during that hour they just start making everyone a winner. Those are just two theories as to why.
Anyway, what I do is play a code. If I lose I don't play again for ~10 minutes. However, if I win, I start playing as fast as I can--I don't even bother to stop to collect my download code; I just save it to my account so I can play again ASAP. I store up codes in my account so I don't have to enter new ones as I play.
Here as the results of my last 44 plays:
-win five times in a row
-lose once
-win once
-lose twice in a row
-win three times in a row
-lose once
-win six times in a row
-lose three times in a row
-win once
-lose three times in a row
-win four times in a row
-lose once
-win once
-lose once
-win eight times in a row
-lose twice in a row
-win once
That's 30 wins out of 44 codes--or 68% win rate.
I'm willing to bet that I would have won several more times after that last one had I not ran out of codes.
The trick is to find the "winning section". Unfortunately, this trick really only works if you have many codes to play at one time. If you're only playing a handful you might never find the pot.
Again, I haven't really tested this, so it could have been a fluke or it could have been related to the site running out of Wii codes. Play at your own risk.