Ok folks, here it is! Through much exhaustive research, long distance phone calls, a good poker face and some sweet talking, I have discovered the truth on actual dealer invoice prices on European Delivery E46's! For those of you who are interested...
Subtract $1770 from the US invoice price for a 328i.
Subtract $1435 from the US invoice price for a 323i.
Naturally, the destination charge must be figured in to this equation. These figures were verified by two dealers in totally different parts of the country, so I have reason to believe they are accurate.
Hope this helps some other folks out there! Happy negotiating!