Ignore key signature?

[Urs Liska]

I have an issue with writing parts without key signature, i.e. trumpets, 
horns and timpani.

I know that I should simply _not_ write a key signature to achieve the 
desired effect. The problem is that due to the infrastructure of my 
current project it seems inevitable that key signature (i.e. \key 
commands) slip into the parts automatically.

My first thought was to \omit the time signature, but that doesn't work. 
Consider the following example:


\version "2.19.14"


{

   \omit Staff.KeySignature

   cis''1^\markup "no key"

   \key d \major

   fis'^\markup "D major"

}


the cis is printed correctly, but the fis doesn't get a sharp. Obviously 
\key d \major is effective even if the key signature isn't printed. The 
problem of that notation should be obvious from that example: The 
performer will of course read f' for the second note.

So the question is: is there a way for a voice/staff to completely 
ignore the \key command?

TIA
Urs