It is official now: There is positively no way to hide extra fonts from USE_ALT_FONTS on PW unless you jailbreak. The button I intended to write for KUAL did not happen either as I was busy exploring a loophole to hide the fonts without jailbreak. Turned out to be non-functional.
Good news though for everybody that is jailbroke:
Jimmy-Jim wrote the button. See
his post.