The idea would be to have an auditorium, where you would come in and sit and do nothing, and be paid the minimum wage when you leave based only on the amount of time you spent in the room.
Individuals would be free to accept wages lower than the minimum wage for outside jobs, but employers would have to compete with that minimum wage for employees, so any lower wages offered would have to compete in other aspects -- pensions, tips, benefits, opportunities for advancement, etc.
Because this would require physical presence, it would naturally be self-limiting in some aspects of abuse; you can "sit" as many or as few hours as you wish, but you cannot use that time for other productive work, so there's a natural fall-off of benefits as you choose to work instead (rather than an artificial administrative "cliff").
There are other aspects which seem very vulnerable to abuse -- why not just sleep there, what about doing remote work on a laptop, what about setting up shop and selling hot dogs in the room, etc. And there are some aspects which seem logistically problematic -- how do people commute to the room, how many rooms do you need, what about people who have disabilities that prevent them from travelling, etc.
But generally all of these seem addressable, and some of them might just be self-regulating by social norms, so that there is a small but acceptable amount of leakage due to abuse.
It seems administrative simpler in some regards than UBI, in that the uniqueness of a recipient is more easily enforceable, and it doesn't just change the y-intercept of the income curve, but rather semi-truncates it, so might be less vulnerable to attempting to extract the income through rent increases.
It also more easily adjusts to location-based pricing sensitivity -- it's totally reasonable for a place like SF to have a higher "minimum wage" than a less expensive city (just as minimum wages can float from state to state), and the requirement for physical presence makes it harder to game this.