While you said that automated testing isn't feasible, I feel that you might still benefit from them. Automated testing suites like mercury http://www.mercury.com/ can do quite a bit. I don't think this is a substitute for real human testing, but it may cut down on the amount of "its working here" problems. Moreover, it will allow you to develope a set of tests that you can run during your future development.

Other than that, it seems like you need to identify your customer base. Once you have that, give them some free stuff and you'll be surprised at how many will want to try it. Get your marketing dept involved. If this is a potential big thing, make them do their job :D.