A random suggestion, then: perhaps try selling it for a few months, and if the number of sales starts to tail off and you still feel uncompensated, set a fundraising goal at which you'd release it open source?

As others said, I'm more interested in donating (and helping to persuade others to) to make it available for everyone than I am in buying a copy.

http://www.indiegogo.com/projects/tern-intelligent-javascrip... is an example of successfully raising money for a javascript tool, although in that case the money was raised before the work was finished.