giant bar numbers

[Curt]

For film scoring, it's common to want giant bar numbers in the middle of the 
score.  Does anyone have ideas on how to center bar numbers above a bar, as 
opposed to them being aligned to the bar line?  With that, I'm thinking I can 
create an invisible staff that has no engraver except for the 
bar-number-engraver, and then giving it a very large font.  It'd be just above 
Violin 1 in the orchestral score.  I think that way they'll be nicely aligned 
vertically - I'm just not sure how to center them.

Thanks!
Curt