Another "off the wall" idea could be to have students read and critique chapters of each others' thesis. I took a course in grad school where everyone was a reviewer of everyone else's paper. This could create some positive peer pressure to create a good version of the draft. And, making someone give feedback on someone else's work, can make them think about what someone is looking for in their work.
It may be that some students just don't want to do the thesis, and nothing you can do will help them write a better thesis. However, as an optimist, I have to believe that if there are such students, they occur at a rate far below 10%.