Another thing you can do is add the restrictions to the name of the shipping method. In other words:
UPS Ground 3 day - US ONLY
UPS Ground 2 day - US ONLY
etc. and then add a comment to the page that tells them to be sure they choose the correct one to not delay their order. Puts the responsibility into their hands for whether or not their order gets delayed due to having to adjust shipping prices etc. This should work pretty good with the new Pro version which now gives us the ability to force the choice so they have to make a choice where before in the Basic they didn't have to and could default to the wrong one.