What about this:
The last one who deposited on that round, would receive a percetage of the remained amount or a fixed amount. It definitely would not stuck like atm.
I would do it in this way:
We would stake an amount of 2BTC at the beginning of the each round, before any payout. Then the last one who deposited 1 btc on that given round would take back 2btc as reward. This would be a huge incentive for players to deposit even at the end of each round. Because at the current stat weeklyponzi is basicaly just a 3dailyponzi.