If I had to raise a bunch of money for a project, I'd start out by doing what the PAC team has done, and what fundraisers have done forever -- contact all the rich people and companies and foundations I could find that might possibly be interested in supporting that kind of thing.
The next thing fundraisers tend to do is open the campaign to smaller donors. These people don't get buildings or rooms named after them, but they do get to put their names on bricks and seats and such, and they feel involved and, in aggregate, chip in some real money.
But what if there was a technology that allowed you to do that public phase in a much bigger way -- to throw fundraising open to the whole city and county?
Could you raise $1 million that way? Maybe. Maybe you could do more. You might be able to find 1,000 people who would give $1,000 apiece, and many more at lower levels (and some at higher levels, too). Seems like kind of thing that would bring out matching challenge gifts, too.
And in the process you would build community support and a real sense of ownership for your fancy downtown music hall.
It won't get you the full $20 million you need, but it would jumpstart that effort in financial and political terms.