Hi J.,
I have twins who are almost 3. You could be living in our house sometimes. I have the Love and Logic book too. The one choice that seems to work the best is to offer them the option of A) talking nicely or B) going to their room until they are ready to be sweet. That is what we do now, but for a while it was simply "That hurts my ears when you talk like that. Please take your mouth to your room. You can come out when you are ready to talk nicely." They usually go up to their room, wait a few minutes, then come back down. All I usually have to say is "Are you talking ugly to mommy?" and I quickly get a "No" becuase they know what is coming.
I'm not sure if I'm following the L&L "rules" exactly how they should be, but we have had a decrease in the amount of snotty-ness in our house. Good luck!