If you select Contact Sheet in the Style submenu, you can select how many photos you get per row. With a bit of trial-and-error, you might be able to match the passport sizing requirements. Sorry, that's a crap workaround. 😱
just use PS to resize it, oR preview may have a sizing thing built in. you should be able to change the resolution to say 200 x 150 (example) in iphoto when exporting then just print in preview as original size... that might work. I just don't know the exact resolution/inches of a passport/id picture.