The name of the instrument is... primo :)

[Alberto Manuel Brandao Simoes]

Hi again.
I'm typesetting four hands music and it is common to have before the
piano stave the string 'Primo' and 'Secondo'

I've tried:
\score{    
    \context PianoStaff     <<
        \property Staff.instrument = "Primo " 
        \context Staff = up    \primoUp
        \context Dynamics = dynamics \primoDynamics
        \context Staff = down  \primoDown
    >>
    ..

and some other combinations but I can't put it OK. Ideas?

Thanks
Alberto