Short answer: yes, or pretty close.
Basic template:
top = {
\repeat unfold 4 { b'4 }
}
mid = {
\stopStaff s1 \startStaff
g'4^\markup "Tutti" 4 4 4
}
low = {
\clef bass
\repeat unfold 4 { e4 }
}
words = \lyricmode {
hel -- lo good -- bye
}
otherwords = \lyricmode {
new staff is here
}
\score {
<<
\new ChoirStaff <<
\new Staff \top
\new Lyrics \words
\new Voice = "new" <<
\override Staff.TimeSignature.stencil = ##f
\override Staff.Clef.stencil = ##f
\override Staff.KeySignature.stencil = ##f
\mid
>>
\new Lyrics \lyricsto "new" \otherwords
\new Staff \low
>>
>>
}
I achieved the following given the image you provided. If I look further, there's probably a way to create that spanner bar between the top and bottom staves where there isn't one previously.
Long answer: it seems to me that if you're going for an unconventional manner to instruct all voices to sing in unison (and not octaves), then there are less strange ways of showing it. For instance, if the voices need to be in unison in the middle of the page, why not continue two staves until the line break, and then cut it down to one staff and write something like "all voices in unison"? That would seem to me to be less ambiguous.
Perhaps something like: