what's the most "efficient" way of doing this?

[Kieren MacMillan]

Hello all,

Let's say I've got a series of RehearsalMark and MetronomeMark objects. I want 
them to appear at (e.g.) three places in my score:

1. Above the top staff of my score, at "full size";
2. Above the string StaffGroup (about 2/3 of the way down the score), at "3/4 
size"; and,
3. Below the last staff of my score, at "3/4 size".

My score is frenched, so the top staff will not always be the flute, the top of 
the string StaffGroup will not always be the Violin 1, and the last line will 
not always be the double basses.

I want to find the sweet spot of engraving efficiency, both for me (the least 
work) and for Lilypond (the least impact on performance). I've got two basic 
ideas on how to do this:

A.
    A1. Put the RehearsalMark and MetronomeMark objects in a separate variable 
(using either skips or tags).
    A2. Add this variable (only) to contexts at the appropriate points in the 
score.
    A3. Add this variable to all other contexts (for parts, etc.).

B.
    B1. Put the RehearsalMark and MetronomeMark objects in the main global 
variable (which also includes \time, \bar, etc.).
    B2. Create a MarksOnly custom context, which only has the engravers 
necessary to show RehearsalMark and MetronomeMarks, and let it "filter out" 
everything else from the \global variable.
    B3. Put the \global variable in all other contexts (for parts, etc.).

C.
    C1. Move the relevant engravers from the Score context to the appropriate 
contexts in my score.
    C2. Tweak the placement of the grobs as necessary.

Thoughts?

Thanks,
Kieren.