How to move from one grandparent to another

[Rune Zedeler]

The following example should illustrate my problem:

\score {
    \notes \relative c'' <
        \context StaffGroup = up <
            \context Staff = sone { s1 }
            \context Staff = stwo { s1 }
        >
        \context StaffGroup = down <
            \context Staff = sthree { s1 }
            \context Staff = sfour {
                c4 \translator Staff = sthree
                c \translator Staff = stwo
                c \translator Staff = sone
                c
            }
        >
    >
}

I would like to move the voice to the upper two staves instead of new 
staves.
How can this be done?

Han-Wen, you were thinking about redefining the uses of "translator". 
This problem should so very definitely be taken into account.

-Rune