Once the dust settled, do the same with the next project.
From the maintainer side it can be a bit tricky though. Typically the finance will want to pay another corporation, so the maintainer would need to create some sort of legal entity to bill with. The other potential issues would be around legal liability in case something goes sideways. You run the risk of getting sued if you don't provide a level of support that some corporate client is expecting.
It's an old idea, and a proven one. Anecdotally, I made my living as a such a hire for nearly a decade.
Another good plan, mentioned elsethread: have your current devs contribute. Opportunities to contribute always arise, and contributing is in the company's interest. The only thing typically standing in the way is codifying an open source policy (which is a good idea for large organizations.)
I'm aware of various attempts to collect payments or offer support plans but I don't think anyone's hit a combination which is as corporate-friendly. Everyone understands the idea of paying for support and it's usually much easier to give six figures to one party than 3 figures to a dozen projects, _especially_ when the latter doesn't get you some kind of guaranteed benefit easily explained to the accountants.
We use a ton of FOSS software. We pay thousands per month to AWS, Datadog, etc... but nothing for the "free" software we use.
People are generally in support of the idea, but then it falls away as a priority, and there's the question of which projects to fund and for how much. We'd have to talk to the finance department, figure out a budget, etc. So it doesn't happen.