The only solution is reputation and selling to the public domain, instead of to individuals:
if people like your stuff, you'll have a reputation because of what you made in the past, then you can offer to release your next project to the public domain if some crowdfunding goal is met.
if people like your stuff, you'll have a reputation because of what you made in the past, then you can offer to release your next project to the public domain if some crowdfunding goal is met.