I have been using this with my current site with no problem at all, thanks for the great mod!!!
Now I am upgrading to 1.3.8a and when I installed this mod everything looks fine, but the option is not available at checkout! I have unistalled-reinstalled and checked all of my settings.
Any idea? I am using fast and easy checkout, don't know if that would make a difference (but it works with 1.3.7 with FEC)