I don't feel like what you've described so far is misbehavior. She's actively engaging in her own learning. However, in my experience, many teachers are bothered when they don't have perfectly obedient, controllable little students. Have you sussed out whether or not these incidents are actually impeding her academic process? Or are they perhaps just irksome for the instructors because they prefer more compliant children? Is it because her behavior is more obvious to the teacher than some other children's method's of not paying attention?
I'd say she's displaying a attention span that's just fine (by being able to focus on a book for a long period of time). Some children despise reading, or simply won't do it in long increments. She's able to keep reading, despite the fact that she's no longer required to be reading. So I'm not sure she has an attention problem at all.
However, she likely has an interest problem. Teachers talking/explaining things can be dreadfully boring. If a student is put in a position of passive learning (such as lectures), then their attention is going to wane regardless of age. Just because a student is upright, eyes front, and books down doesn't mean they're actually paying more attention to the teacher than the child reading a book. The only difference is one student is zoning out in a way that's hard to judge, and the other is visibly not tuning in the the teacher. The latter is usually more upsetting for the instructor than the former, despite the fact that they functionally have the same result.
I bring this up, because teaching your daughter not to engage in side-activities (like reading, or doodling) may just lead to her zoning out in a way that doesn't draw the teacher's ire, but also doesn't have your daughter paying any more attention to the class. If material is boring/uninteresting/going on too long then sometimes you just can't help zone out. It's how our brains work.
Thus, I'm not sure your daughter has an issue delaying gratification either. Yes, she may be engaging in more interesting activities, but there's nothing to say this is because of poor impulse control. Can she wait until after dinner to get dessert? Can she wait to get home to open a new toy? Can she accomplish a task for some sort of reward? If you can answer yes to these questions, it's not really a gratification problem.
However, I think there may be an actual answer to your question (even though I'm not convinced your daughter has issues):
The teacher needs to structure a more engaging learning environment, with more opportunities for active learning, for the children to let out some of their energy, and to allow for the differences of willful/independent children (which are positive attributes, although some teachers will tell you otherwise).
You can do as much training as you'd like at home, but you're not likely going to be able to replicate the environment of a school classroom. Since you also can't be present when these situations occur, it really ends up being the teacher's responsibility to handle.
Fear not! It's not completely out of your hands. You can certainly offer some suggestions to the teacher to help them guide your child to a state of optimal learning.
Here are some ideas that may help:
Otherwise, I feel that what you can do about your daughter's delayed gratification has already been answered best by Christine Gordon in the question you linked: https://parenting.stackexchange.com/a/6356/11394
She mentions that you should work on developing your daughter's ability to be intrinsically motivated by different activities, and offers some suggestions on how to do it.
This solution won't necessarily improve her classroom performance (especially if the issue is the classroom). Nevertheless, teaching a child to be satisfied by intrinsic motivation will help her be more successful with studying, homework, chores, self-learning, and work (when she's old enough).
A great book on how to encourage intrinsic motivation, and the drawbacks of extrinsic motivation, is "Drive: The Surprising Truth About What Motivates Us" by Daniel H. Pink.