In Zkopru, withdrawers can request an instant withdrawal by setting the instant withdrawal fee for each withdrawal note. Then, anyone can pay in advance for the unfinalized withdrawals and get the fee for them.
To request the instant withdrawal, the owner generates an ECDSA signature for her note and broadcast it. Anyone who has enough assets to pay can pay in advance for the withdrawal using the signature. Once Zkopru includes the transaction successfully, the smart contract transfers the ownership of the withdrawal note to the payer. Finally, the prepayer withdraws them after the finalization.