Do you want to cache it on a personal proxy server or on your client?
But the whole thing makes no sence to me, because it may be possible that you don't get credit for crunched workunits you downloaded long time ago (someone other may have crunched this workunit as a random block). I think it's better to crunch online or update buffers every day or two.
Caching on proxyserver: erm, regardless what you set in your config-file, it won't go higher that 1000 workunits (I think that was the number, when I crunched RC5-64 long time ago). A lot of clients must uploading (and you may not restart your proxy whilest this time) results and so the proxy notices buffering more WUs would be a better idea.
Caching on client side: config --> buffer and buffer update options --> fetch work threshold --> RC5-72=[value]; or edit that lines of your dnetc.ini
Code:
[rc5-72]
fetch-workunit-threshold=3000
save your changes and restart. I don't know if the client really downloads that much WUs
As I said it isn't recommend buffering high amounts of workunits to crunch offline a long time.
Please correct me if I talk :bs: