I still would like to see someone cheat the system, all the talk is about how we can cheat the system if it is so easy why isn't everyone coming to the site and cheating you could be making all most 2 BTC a day ($800+) a day?
The thing is taking the client seed determining what its going to end at, then broadcasting that exact txid on blockchain is too hard.
But you have pointed out how its not 100% full proof we understand that now. But i still challenge you to cheat the system your self (as you claim its so easy to do) or give us a better method.
While the described attack is relatively easy, there is still some effort involved and considering your game's current revenue it is probably not worth the time of anyone that has the knowledge necessary to carry it out. But if your game gains any traction and your system remains in this form it is virtually guaranteed that someone will attempt to take advantage of it, if only to prove a point.
Another point to consider is that cheating the system is not possible for an external attacker in the event that the house is already cheating by picking beneficial transactions.