afaik what you want can't actually happen. The CFW makes everything that runs on the system believe the SD is the NAND, and thus anything that runs within that CFW can't really tell which it is running from. And even if it is possible, it's not necessary because there are much easier ways to tell. Like the method I stated before where you just set a default theme (or no theme) on sysNAND and then set emuNAND theme to something else that you actually want to use. If you do that it's extremely easy to tell which you are in straight from the home menu.
Not trying to be rude, but you just don't like the answers you are getting, which in short are "it's not worth the time and effort to develop"