For many of the things that people might want to do, a "patronage" model isn't so bad either: the creator demands $1000 for the work behind the link; people can leave an e-mail address and pay anything from $1 to the full remaining price, and will be notified as soon as the work is available.

I think this has tons of value, almost like a mini-kickstarter without the need to advertise for a kick for communities of people (forums, etc) who want new features or some kind of quick bit of work done.

Disable direct links and proxy the content, that way you can create unique URIs for every buyer. Then you can do all sorts of things like add a watermark on the content page containing the credit card number of the buyer or just add expiration time to the links. That'll limit sharing somewhat, although I don't think it's a huge problem.