Actually there is an easy way to do this. an INDIVIDUAL from the project invoices. they act as an independent contractor. They invoice for "support". You don't need a COMPANY to send an invoice and bill someone. An individual can do it. (Companies exist to take advantages of tax and ownership as well as separation of obligations vs the individual). In this case there are no obligations (or shouldn't be).
So now the individual has gained $5000. sure - they must pay tax on it. let's assumed 30% that's $1500. Put the $1500 aside, then give the $3500 to the project - if it has an existing legal non-profit entity. There is no laundering here. You do it in the open. you use fully documented bank transfers. This wouldn't trigger any money-laundering laws I know of. At the end of the tax year, declare the $5000 as "extra income", pay your $1500 in taxes and the project has $3500 now to spend (on a new server, storage, equipment, bug-bounties etc.).
Even better if the project has members who are ex-pats. I know that where I live, only money earned IN the country I am in (Korea) is taxable by Korea, *OR* if i remit money I earn outside Korea back to Korea. If I earn money somewhere else, Korea LEGALLY makes no tax claim over it. As I am not a US citizen... I'm not beholden to the US govt for taxes, regardless of my location, So actually... I can legally earn that money tax-free, so long as it never comes into Korea... so I wouldn't have to put aside $1500 (actually in Korea the tax rate for me is more like 16% - complete flat tax, not 30%). So it's possible and easily done. An invoice is easy to do. I have templates for them...
I think the issue here is that the projects contacted don't have enterprising members who have done contracting/consulting before... etc. etc.