I do a variation on this to pay my mortgage and feed my cats...
I run airwindows.com and write audio software for musicians and mix engineers. Some of the earliest stuff, a decade ago, was GPL, and I continue to be willing to talk freely about pretty much anything (talking tech becomes a turn-off for musicians, so I don't often get into it as a rule)
What I did to start making (some) actual money versus 'no money' was this:
Pick out some of the stuff, including everything that was GPL, and make it 'free beer' free. Since it's all mine, anybody wanting stuff added to the GPL pool can have it for the asking- it becomes dual-licensed because I'm not actually drawing from the GPL pool. I ended up including source for the public domain FreeverbCJ, and RMSBuddyCJ is GPL- but when I did closed reverbs I didn't even draw on the PD Freeverb stuff, I wrote up a much less object-oriented framework from scratch based on general reverb concepts. I don't use graphics code so I didn't draw from RMS Buddy for anything closed.
Pick out some of the stuff to be closed, and put it out there in such a way that you basically pay for access to get the widget in the first place. Kagi has a nice little setup where they can sell digital downloads with URLs that are temporary- there's no one fixed URL given out. I also keep prices at maybe a fifth of what the big nasty copy-protect guys are doing, and consider sales to be a lifetime thing- I'll support what I put out so long as I'm alive to do it. I keep it real simple so I can do that- if Logic changes and breaks existing plugins, it's on me to make it right for everybody I've sold to, since I haven't given them the code to fix it themselves :P
Lastly, I passionately believe that selling closed source software has to be a 'pull' rather than 'push' model: some people seem to think because they can have an idea, people are OBLIGATED to pay them. I think that has to be earned. I think it has to be earned by behavior. I wouldn't pay for someone to come and kick me in the teeth, so why would I pay for someone to come and shut off my software or audit my shop to see if I'm taking more than I ought? What makes that THEIR bailiwick? (I'm talking of Waves and their raids on studios.)
My stuff's copy protection is the original source of access- Kagi charges for the initial download, there's no place (or shouldn't be) saying 'download anything, pay if YOU feel like it' because why should it be that easy when I've repeatedly worked with people over the years and given refunds if they made a mistake? The effect is the same (except I pay a fee on refunds and chargebacks), it's just that you don't get to have the full product just on a bored random whim. There are demos for that ;)
Once you do have it, I start looking like the open-source world again: there is no dongle, there is no serial #, the bit of software is just the bit of software. It's not even the unlocked demo- there is no unlock to the demo, the product is the same code with the demo stuff (an output muting at intervals) commented out and a recompile. It's a black box like most commercial closed software, but it's a box without locks or traps or alarms- it just sits there working, you can back it up, and the only thing that prevents people from widely filesharing my work is earned respect. I WILL not add stuff that would get in the way of a real user just to fight 'pirates' when I could give a sh*t and earn some of their respect instead.
I also have the following unusual attitude: digital stuff not being used doesn't exist. If somebody who doesn't mix downloads three of my best, costliest (alright, $60) plugins and puts them in their Components folder and then never mixes a song- as far as I'm concerned, there is no 'theft' because it's meaningless. It's the same with a lot of mp3 filesharing, with obsessive warezing- hell, I have legitimate books, legitimate programs I don't read or use. How much more with the guy who's a big collector and eeevil w@r3z puppy and doesn't actually create anything?
I would hope if I could encourage a guy like that to create, they might be so moved they'd turn around and re-buy the three plugins- now that would be a donation I'd find really touching :D but I'm not going to wig out over some guy hoarding digital bits like Smaug in a cave, knowing he has them and doing nothing. That's more sad than hurtful... if he tries to be important by mirroring my site as warez and promoting it, I'd have plenty of recourse to politely shut him down, which is all I'd want to do anyhow.
I'm not as big a fan of Kickstarter, though I've seen it be appropriate: seems like that's useful for clear projects requiring hired work, but I don't think it's a substitute for just entrepreneurship in general. Sometimes it's not about Tom Sawyering, sometimes you just have to take a risk and do something.
Ack, what a TLDR- well, you mention 'donation business models' around me and you get an earful. I beg tolerance for the fact that I'm an old fart, and it's good to drop by Slashdot again :)