If you're going to get the live action feel of a spreadsheet, you're almost certainly looking at more than just ruby; you want a bunch of live processing, most likely in JavaScript.

There's nothing native yet, and I don't personally know of any plugins. My first guess is that some sort of embedded plugin would be the fastest approach, but it partly depends on how extensive the tables are. If it's really simple it might be something you could build fairly quickly in javascript, in which case you wouldn't need to install anything on a server, and it should be easy to implement regardless of your server architecture.