I think there are no casinos that allow betting that amount, I just take a look at roobet and the max win on dice is $50k , that's a lil more than 2 btc.
Maybe you can place a bet like that with other users in the forum, the result from the bet could come from a future block and if the founds are collaterized then this could be fair for all.
No casinos in the right mind would allow that right off the bat. Even 10% of that is enough to cause most owners to sweat bullets. :p