Essentially, by keeping the basic income guarantee sufficiently low that most people don't want to do that. Note that having everyone want to work is not necessary or even necessarily desirable, you just need to be able to maintain a low enough dependency ratio that the working people don't have to sacrifice much more than what they gain from such system.

I personally think that the employment market for next few decades will continue to be characterized by endemic structural unemployment. We will continue to destroy jobs faster than they are created, through automation and efficiency improvements. What's going away especially quickly are the "middle-difficulty" kind of jobs -- between highly trained specialists and burger flippers. For a simple example, self-driving cars will soon revolutionize long-distance trucking. They won't eliminate the jobs completely, but they will significantly reduce their number. There are 3.5 million truck drivers in the USA. How do you retrain a 55-year old truck driver to be a software engineer? If you can't, should he go work at Burger King for a much lower wage instead? Maybe as a society we could just allow people like him the possibility of not working at that point?