Adding an instrument for only a portion of the score

Perhaps this has already been discussed, but in working with a lot of the music I deal with for my choir, there are often solo parts that would be best handled with a separate instrument (voice) but are present only for a relatively small portion of the overall score. A related issue are pieces that have sizable piano intros or bridges where there are no voice parts and it would be nice to not have to carry the SATB instruments through those portions of the score.

My options now seem to be to either, 1) add the solo voice instrument for the entire score, or 2) add the solo as a separate voice in the appropriate instrument line where the solo occurs.

The problem with (1) is that it is very wasteful of score space and, for a relatively large score, drastically increases the number of pages required. The problem with (2) is that it clutters the reading of the score, can cause conflicts with lyrics, but is more true to the spirit of the composition.

I would imagine that this would be a complex endeavor as it would break any assumptions of a constant system height throughout the score, but it would allow creation of a lot of scores that are more true to the work.