I am also guilty of taking risky trades which I would have never done with my live account. I agree with Carlos' suggestions and add following to make challenge as close to reality as possible.
Limit position size to Max 25-33% of equity (Can DAS enforce?)
Limit Max Loss 2% of equity per trade (Auto stop), example: For $30,000 equity. Max loss $600 per trade
Limit Max Loss 10% of equity per day (Auto stop), example: For $30,000 equity. Max loss $3,000 per day. This way, PDT rule triggers after two consecutive days of losing @ Max Loss
Use IB Fixed rate commissions ($0.005 per share, min $1 per trade), No ECN fees.
These limits may seem too restrictive for game trading, but are very generous for real life trading.
Also, I think it will be good idea to allow people to post their trade log for challenge everyday so we can learn from each other's trade activity.