Alex,
You could also remove the branded favicon entirely from the x-payments install, right? No need to tell people to remove it if it's not there in the first place.
I still think "chaining to a tree" is a reasonable penalty for a developer who puts their own branding in a product destined for ecom.
PS -- I have not been able to purge the favicon from my browser cache even though my fvicon has been there since day one. Maybe I have to clear the x-payments cache at the server?