Not sure on the viability of it, but couldn't there be something in place that states that fines can only be levied at a maximum 10%/month of the UBI?

So if you get a parking ticket (presumably <1% UBI), you can just pay it, but if you get a large fine (20% UBI), you'd pay it off in two monthly payments of 10% each.

You'd probably need something in place to intervene if someone's constantly paying 10% every month due to multiple fines to prevent people racking up daft amounts of fines and just 'living on 90%'