KLM Elites get free upgrades on NW domestic metal, all you'll need is a european address to get into the KLM program.

MilesBuzz seems like the appropriate place for this.

Northwest provides complimentary upgrades to elite members and companion upgrades to gold and platinum members on domestic flights, including to/from Canada. This is from any fare and it's on a space-available basis. Silvers can get confirmation the night before their flights, golds up to three days prior and plats (I believe) up to five days prior. By reading the board, success in receiving upgrades varies but I have to tell you that as a gold elite, it is VERY rare that I don't receive an upgrade to FC. I've even received them on standard (minimum miles) award tickets. Much of this right now may be due to a softer market for business travel, but if there is a more consistent program in the industry for domestic upgrades from even the lowest fares, I'm not sure that I know what it is.