Set up an Apache mod_proxy from port 8080 on your server's localhost to a vhost at showoff.yourdomain.com.
You'll have to make sure to build your app to not make any assumptions about where it's running (ex: links to "http://localhost:3000/path), but you should be doing that anyway.
With just the most minuscule bit of initial setup a simple bash function using just SSH can replicate all of the functionality (and more) of showoff.io, with just as much ease ('show 3000 subdomain') but hopefully the upcoming features will make it a more viable proposition... :)
Then again, I'm quite happy with a VPS setup since I get all of the extra benefits of having the server around...
> You have to have Apache setup (which, when developing a new project, you may likely not have even reached that point).
Showoff project is definitely cool, but instead of apache, nginx installs in one command and can easily proxy like this with about 10 lines of easily googled config using 1/10 of the resources on a simple prgmr account or the like.
You'll have to make sure to build your app to not make any assumptions about where it's running (ex: links to "http://localhost:3000/path), but you should be doing that anyway.