If by prizes you mean materialistic stuff then no. If you could ie win cash prizes then through cheating you could earn money. The only way to do this properly is to have a place where people can go to and play there over LAN. Otherwise prizes would be given rather unfairly.
However if people would still agree to do it then there should be an entrance fee of say $4 and a prize money of like $50. Then people would enter at their own risk...