Multi-Site Theme/Customization?

Hey there guys, I’m experimenting, with Mult-Site option. Attempting to create a website offering pretty much a similar service of WordPress.com. I was wondering if there is the theme or plugin, that makes the Sign-Up form customization alot easier than hardcoding it in.

For example the way http://edublogs.org/signup/

and https://signup.wordpress.com/signup/

Are setup…if so could you please direct me towards such a plugin/theme.