Re: I want to *force* spacing

[Robin Bannister]

>  I suppose I'd like a filler that does *not* take up duration

You can use a breath mark for this 
http://lilypond.org/doc/v2.12/Documentation/user/lilypond/Curves#Breath-marks 
and then make it blank by overriding #'text or #'transparent. 

gap = {
 \once \override BreathingSign #'text = "" 
% \once \override BreathingSign #'X-extent = #'(0 . 2) % to make it wider
 \breathe 
}


Cheers,
Robin