Total invisibility

[Gilles Sadowski]

Hi.

I'd like a "Voice" to be totally invisible (i.e. taking up no space) while
retaining midi output.
The purpose is to add the drone to a bagpipe part. Currently I've done
something like the attached file.

The problem is that the "\drone" takes space and pushes the violin staff
downwards. Also (in the complete file) I get a lot of:

[...]  warning: ignoring too many clashing note columns

What would be the incantation to make those notes totally "neutral",
graphically speaking (and, if possible, make the warnings disappear)?
Or is there another, better, way to achieve this?

Thanks and best regards,
Gilles

test2.ly
Description: Text document