You can simply see if it is going well ( IP translation ) , using an external web-page to see what IP are you shown . If you are shown the external IP , it work's ...
What do you mean by PAT , unde Linux systems ? Do you mean CISCO router's PAT ? I think you do .
You can simply use MASQUERADE ( MASQ ) - depending of your kernel version / iptables version or NAPT ..
PAT is the process , of translationg TCP/UDP pachets' IP address ..
I don't think you can , you must ( if you want ).
Cheer's !