My advice is that if you are really serious about this, you should only release the demo software to people who have signed a legally binding non-disclosure agreement. And be prepared to go to court if they breach the agreement.
By all means, obfuscate your demo application, etc as well, but don't imagine that this will stop a determined hacker from discovering the "secret sauce" in your application. It is not possible to prevent this, in theory and in practice. Piracy is inevitable if you use the pay-for-license model of monetizing your software.
(Actually, it is theoretically possible, but only with a totally secured platform like TPM. And that ain't an option for you. Trust me.)
