Thecool1 is correct. If you want them all to come thru on the same IP address, they'd need to flush to the pproxy from the same machine. You'd need to either setup a pproxy of your own, or you could sneakernet (use a floppy) blocks from one machine to the one that would be doing the flushing.
Are you getting two IP's because you have multiple IP addresses from your ISP, or because you have assimilations and machines on different ISP's?
BTW, Denis, what's a "pagina"?
Russ, NCNE