Create a smart contract where anyone can donate. Donations are invested by the contract into DeFi or PoS. Earnings are used to buy UBI and the UBI is immediately burned by the contract. Such a contract could be created by anyone independently of Democracy Earth and/or managed by the DAO. In fact it would be best if there were multiple contracts with different investment models and governance for the funds. (Key variables are: what to invest in, whether the contract is upgradable, whether the donor can stake/unstake to move the funds as the investment landscape changes.) All doable on Ethereum today.
This would create a sustainable deflationary pressure on the UBI token or think of it as creating constant demand for people who want to trade their UBI for other tokens.
Donors could make pledges for when registered users hit different milestones to incentivize vouching and growth.
This would be a simplification of what GoodDollar does. See the
DonationsStaking.sol contracts for working examples of something similar:
Inspired by GoodDollar and this tweet: