Gregorian "half bar line" in normal mode

[Tom Dickson]

I'd like to get a half bar similar to the one you get in Gregorian  
mode but without switching to Gregorian mode. I assume that this can  
be done, but I'm not sure how.

Specifically, I'd like to be able to use \divisioMaior in normal mode  
- could I simply find the definition of it in gregorian.ly and copy it  
over?

-tom