Thanks to diddy81 for his custom themes and tools, it's possible to install custom themes on vWii! This wasn't originally possible by normal means, but thanks to this script you can easily inject a theme straight to your vWii. I take no credit for anything in this tutorial, I am simply projecting his work into a tutorial you can follow. His original post is...
[Tutorial] Installing custom themes in vWii
[Tutorial] Installing custom themes in vWii