\grace at time change again

[David Bobroff]

Wrestling with grace notes at time changes again.  Graham posted
something about adding another \time and \partial but I didn't really
understand how to use it.  There is a model of my problem below.  I have
my time signatures all in a block and then the music for three different
parts in their own definition blocks.  I can get the grace note to line
up the way I want if I:

1) Place a \time change in EACH part at the appropriate place, and

2) REMOVE that particular time change in the time signature (ts) block.

Is there a better way to do this?  Doing it this way is probably
possible.   I would simply have to place the time changes for the
measures starting with \grace in each part, comment them out of the time
signature definition and keep the right amount of s(kip) values in the
time signature block where the time changes were being specified in the
separate parts. [Was that sentence long enough?]

-David

ts = \notes \context Voice {
    \time 4/4 s1
   % \time 3/4 % This must be commented out
}

up = \notes \context Voice \relative c' {
    g1
    \time 3/4 % This must be here to work
    \grace a8 % This must be here to work
    g2.
}

mid = \notes \context Voice \relative c' {
    R1
    \time 3/4 % This must be here to work
    \grace s8 % This must be here to work
    R2.
}

dn = \notes \context Voice \relative c' {
    R1
    \time 3/4 % This must be here to work
    \grace s8 % This must be here to work
    c4 d e
}


first = \notes {
    <<
        \ts
        \up
    >>
}

sec = \notes {
    <<
        \ts
        \mid
    >>
}

thd = \notes {
    <<
        \ts
        \dn
    >>
}

\score {
    \notes {
        \context StaffGroup {
            <<
                \new Staff {\first}
                \new Staff {\sec}
                \new Staff {\thd}
            >>
        }
    }
}