Andrew,
If you don't want to extract previews, then don't.
Some people do - for them, it is possible.
PS - jpeg encoding is better than one might think despite being "8-bits". The reasons for it are beyond the scope of this thread, and I don't understand it well enough to explain anyway, but we all have vast experience with jpegs: great as a final image output format, but not as an original editing format. But neither I nor anybody else in this thread has been suggesting to edit the jpeg preview in Lr instead of the raw file. Quite the contrary in fact. The purposes for the jpeg are:
* so you have a rendered copy, which you may have worked hard for, before you re-edit the raw in Lr (or in case you never do). That copy can be emailed, posted to the web, used in a slideshow, printed, etc...
* to compare your Lr editing to.
Rob