Basically just use an application to browse the iphone, whether it is iphonebrowser, diskaid, ssh, etc. Find the location of the theme, located at /Library/Themes Take the items of the one theme that you like, and make a copy of it and put it in the corresponding location of the theme that you are currently using. Re-apply that theme in winterboard to see if its what you like.
Sorry I don't have too much time to explain right now. If you need more description I can help later.