With regards to your question, I can only offer some personal reflection. I think that a carrot/whip for reading some given text is a bad idea, unless your objective really only is to make them read the text. Those who feel they benefit from reading already do it. Those who don't feel they benefit will either not read, or not get much out of it, and thus get the whip every time.
Now, for the real reason I'm posting this: Your question raises some counter-questions. I don't mean to sound like I'm picking a fight, and perhaps there are cultural differences here, but some parts of your question seem strange to me.
(I'm not familiar with the school system in which you're teaching, and I don't know at what level you teach, so bear with me.)
1) Why do you keep using a book that most students do not like? They'll be more likely to read it if they like it...
2) Is class time spent mostly on you giving lectures? If so, from the students' point of view, I'd expect you to cover at the very least everything needed to pass the course. I might turn to the book to clarify, or to help me remember what you said, or to prime me before your lecture, but I would not expect the book to be the only source of anything essential.
3) How old are these kids? If they're somewhat grown up (say 18 yrs old or so), assignments and quizes every time you meet seems like a lot of interference in their learning. People learn in different ways, and the sooner they get to figure out how they learn effectively, the better. Offering a lecture plan, so that those who want to can read ahead and prepare themselves is helpful. Trying to force students to learn in one particular way is probably not very effective.
So, yeah.. I do apologize for not answering your question properly, and once again, I don't mean to sound like I'm picking a fight, so try not to take it that way. I'm just surprised by the picture I get when I read your question, but perhaps I'm interpreting things incorrectly due to some cultural bias or something.