Little Miss Manners

Lately, Ela has been acting more and more like a two year old, and they don't call it the terrible twos for nothing.  To combat the frutration we all feel when Ela has a temper tantrum, we've been talking a lot about manners and encouraging her to say those polite words we  all love.  "Please" has been the big challenge.  She doesn't understand why she should have to add an extra word to her sentences when just saying what she wants usually gets it.  So, like all parents, we've resorted to bribery.
Every time Ela asks for something, I ask her to say please, but usually I give her what she's asking for whether she successfully uses the word or not.  After all, I want her to continue to eat broccoli, for example, so I'm not about to dissuade her by insisting on manners at that moment.  However, if she asks for something we don't really want her to have, like ice cream, we insist that she say please first.  This has, of course, led to a few more temper tantrums, but it's also led to a few more pleases.  In fact, Ela now sees please as an automatic pass card.  She seems to think that as long as she says please, the world is hers for the taking. 
On the whole, this attitude works out pretty well.  It means that some mornings, Ela announces, "Eda want eat cereal say please." and I can praise her manners excessively and give her the cereal.  The problem arrises when I can't, for whatever reason, fufill her desire.  If, for example, she askes for watermelon pleeeeeeease, and I don't have any watermelon, we have a problem.  No matter how patiently I explain to her that the words were right but I really can't help her, she takes the rejection personally.  Also, sometimes I just don't want her to have ice cream, or a cookie, or whatever.  If she ate precisely zero of her dinner, I'm not about to give her dessert.  So when she says please in that situation, we have to up the stakes and demand that she first eat her chicken.  She doesn't like that much.  I'm sure you can guess the results.
And then there are the times when Ela forgets I can't read her mind.  She'll approach me repeating "say please!  Eda say please!" over and over, clearly expecting a result.  I'll tell her that I don't know what she wants, but that usually makes her more angry and she ends up having a fit because she doesn't realize she never told me what she wanted.  Those are probably the most frustrating situations for us. 
On the whole, though, I think we're making progress.  Ela says please more and more often without prompting, and sometimes she even throws in a thank you.