Tax-deductible charitable donations are probably the closest way to incentivize the private sector but VCs was more, not just to stay flat and most businesses don't make decisions for "the greater good" over more $$.
Can you think of a way to incentivize private experiments in UBI?
Contracts that guarantee the recipient will pay X% of their income to the UBI source over the next Y years. Claims are that people's creative and productive power will be unleashed. If true, their income will rise dramatically, and they'll pay lots of "taxes" back to the UBI source.
It wouldn't be the person asking for a loan that speculates on them earning enough to pay it back. It would be the entity giving the loan speculating on the person earning so much more in the next few years that the income-percentage makes them lots of money.
Of course, for it to test UBI, the giving entity must not be allowed to decide whether they accept someone or not, that would lead to them picking and choosing, like insurance companies with pre-existing conditions.
However, if the claims about UBI are true, they won't need to, as even the odd slacker will be more than offset by the exploding productivity of the overwhelming majority.
I'm sure Dorsey could fund it, the question is whether he actually believes in the claims of giant benefits and virtually no slackers.
I wonder who their LP's would be...