There is no need to be rich. Spouses stay at home and are not worried if their partner has a regular job. It doesn't have to work for everybody. For starters, find somebody who can handle the risk of you losing your job.
Of course people are happier if they get rich. But that's not what UBI is about. The question is: do people need a monetary buffer to get on in life and become more profitable so that society benefits as a whole?
If that theory is true, then supporting one or two persons will lead to them making more money and being able to support one or two persons in return by themselves. That's a system that can grow, if UBI works.
So, whoever believes in UBI: start supporting one person, and see what will happen.
Society benefits as a whole when we foster the development of proper adults. If the development to making them a net contributor is not done yet, why would we stop?
We support children for years and all we expect them to do is go to school. While a lot of kids could decide to just not work and be taken care of by their family, the vast majority want to work anyway, if only for the fact they want to move out and build their own family.
This may be the key. UBI + Making people go through further education so that they can have the foundation of knowledge and skills to be able to work. Right now, we have a lot of people who go through years of school and in the end it amounts to nothing because no one will give them a real job unless they had the money and a stable environment that allowed them to go to fancy universities instead of being forced to work to provide for themselves. This is a 3 angle attack. UBI + education/training + lowering the barrier for people being able to get a job. With UBI, you will have substantially less people desperate to get any job, so the supply of workers is no longer so high that companies can afford to be picky, because people will be able to tell those companies to go fuck themselves.
That person is guaranteed the durable benefactor and you can see if their behaviour changes and if they are enhanced through this.
If you imagine that UBI would allow people to live with a lower level of stress around starvation, you have to imagine that they would want to rely on that income a decade from now. Saying "find a rich benefactor to decide to give money away" doesn't reasonably test anything meaningful about UBI. I can tell you that people will generally be happier if you give them money one time. Don't need much experimentation to validate that hypothesis...