Having worked in a few open source based commercial businesses, I think the donation model can be tough and unpredictable. The only time I have seen it work is when businesses have commercialized an open source project and then give you a decent recurring donation back in return for your support. So the obvious move would be to just commercialize it yourself. The author does mention this at the end.

If its a small product but with a lot of users, think about a small add on service in the few dollars a month range. If its a more sophisticated product that's a bit more framework oriented, maybe use it as the foundation for project based services and build a consultancy. If its a true product that can be sold, then make a commercial version and start selling it. A lot of times there is a vast vast market out there that doesn't know this is a free open source project, they just see a product which solves their problems and they buy it.