How do I create a little staff/instrument which shows up only for one or two measures for supplementary music/ossias etc

Hi everyone - I have attached a quick jpg image of what I'm trying to do in MuseScore. The little tiny staff with just a few bars surrounded by empty space, but coinciding exactly with the other instruments' barlines, is what I want - take a look please.

I'm working on a two-piano reduction of a concerto and I need to include every now and then a couple of measures of such music which can't be included in the piano part, because we only have so many fingers! This is often done in classical two-piano reductions of concertos, and gives the player an idea of important music, themes etc are being played at that moment. Such information is always included in reduced size notes and staves, but it is not a regular staff like an instrument, because it only shows up very rarely and for one or two measures, coinciding with the bar lines of the other regular instruments, just above or below. Because the information is usually one or two bars long, you would notice that bars are missing before and after, as if someone had just cut and paste only the necessary information. That does not mean that there are empty bars around this music, with rests and no notes - the point is that the empty bars are NOT even there, only one or two bars of actual music are there surrounded by empty space, but placed on the system of instruments (between the two pianos that is)

I can create another instrument and choose small notes and hide any of this instruments staves where there is no music, but I can't hide any empty individual measures and that is exactly what I need to do. Can anyone help me? Up to now I've been using image files in my score and I don't like that.

Shawn, Montreal