well there are a couple of imperfect hacks that would help you. you can use the exe export option, but you could hardwire in an expiry date for the code... so basically check the local datetime and if later than a certain date, you exit the programme, or stall on some sort of flash screen. of course you can hack this my changing the date on your local computer... but that's probably too much hassle for most
you can then combine this with an access code for your players. a fixed code is easiest and for a beta i'm not sure how much more you want. the game play could be captured by a screen capture, the code is probably inaccessible anyway once minified... easier to do from new than to hack.
alternative you could do as above and build in an sql system, but I think you'd fine cross-domain issues that'd you'd need to resolve.
the easiest would be just to build a proper web-app and use a standard login system solution. avoid this exe issue.
again... what is your problem that you are trying to solve? if you're beta testers are not trustworthy... then don't give them something you are not happy for others to see. As several people have told me... ideas are cheap and easy to copy, the execution of your idea is difficult and hard to copy - even when you see it.