I've JUST gone through the same thing this past week!
I applied Frontline between her shoulder blades (per the instructions) and of course she ended up being able to reach it. She got in a couple licks and definitely found it unpleasant, but she's fine. My husband and I watched her for the first couple hours after initial application to make sure she didn't have a severe reaction. We tried to keep her from licking the spot as much as we could, but she still tried to lick it every so often, being repulsed every time (you'd think she'd learn after the first attempt!). This was 2 days ago, and Alpine is just fine. Next month we'll try to put the stuff more on the back of her neck and see if that escapes her tounge!
I read the other day that one lady had to deal with multiple cats that actually would lick the stuff off of each other!