Please Note
This is a serious hack and is not meant for most users.
How To
You must download and install the "blank.app" (package available in downloads) and install it at the following path
/Applications/ .app
Yes, that is with a space. Once installed you can add blank spaces in rSBT to your hearts content. Note that this only works with v0.2.9, and future support is not guaranteed.
Screenshot
The icon doesn't work with 1.1.1, so you get a "generic application" icon. I haven't tried to trick SpringBoard? into using a more creative blank icon yet. Also, the current SpringBoard? patch is somewhat resistant to icon order changes. I haven't figured that out yet either.