Winning the challenges that require you to have the highest number of chips after X rounds can be tricky, but there are tricks other than the cheats that you can use:

Method 1:
The most quickest and cleanest method is to beat them within the first round or two... and that means wipe them of their chips completely. On the lower levels this can be quite straight forward to do, but when you find yourself on the final table, this may be slightly harder since they almost always X-Ray you, and change the cards so that they win...

Method 2:
This is where this method comes in... all you need to do is go all in the first round, and if there are more than two players (including yourself) then you need to come at least second (with a good pair of cards). This'll mean that one of them will end up folding. If you came first great, otherwise what you need to do now is steal chips from the opposing player rather than playing normally. Once you've stolen chips just fold. This'll ensure that you have the most chips and it'll get you to the victory conditions sooner.