show key signature but also alterations

[Frédéric]

Hi,
I'm writing a scale book. I would like to have the key signature but
also an accidentals in front of each note. For example, in d \major, I
would like to print f# c# as key signature and a # in front of each f
and c.
I see 2 possibilities:
1. define a custom Key_engraver which just prints the key and do not
set the alterations.
2. define a special accidental rule that considers that the key
signature is blank

However, I was not able to do any of those.

Any idea?

Thanks,

F