"Is there any other way to get around the 4GiB limitation on the i386 system and use the official Nvidia drivers?" - As far as I know it is impossible. Actually on i386 I cant get freebsd+nvidia to run with more than 2 gigs. (But my mobo doesn have option for memory allocation). PAE is not supported by nvidia too.
The best case is that your friend will be able to use about 3.5G of his memory.
"official" nvidia freebsd support forum is here:
http://www.nvnews.net/vbulletin/forumdisplay.php?f=47