How to retard tcp ack

Hi all!
I'd like to know if it is possible to retard the tcp ack.
I'll try to explain me better:
I am receiving important data through tcp: when I receive this data I don't want to send immediately the ack packet: it may occur that i receive the packet, I send the ack signal and then my system crash: this way the sender will not send me anymore the same datas, having received an ack, and crashing the data just received in my system would be lost.
The alternative would probably be give a sequence number to each packet and after elaborating the packet send that sequence number to the sender: I think this solution would work as well but I don't want the sender to create the sequence numbers for each packet.
So my question is: can I receive the pack, process it, and only then send the tcp ack?
Thanks all people

I wouldn't use the word "retard" in that context ... it's too loaded with other meanings ...
I'm pretty sure you can't control this in Java and I'm even more sure that you shouldn't.
What you want is an application-level acknowledge, and not misuse the TCP-level acknowledge for this. The TCP ACK is soley for transmission control, so that the stream works correctly and the other side knows that it can send some more data.
It was never intended as an acknowledge of the form "I've received your Data and have completely handled it!". This should be sent on the Application Level (i.e. as a separate message in your protocol).

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