How - both in MS and in general - to notate a repeat where some instruments play different things

I have to write a repeated section, where horns play a different background on voltas 1 and 2 under the whole segment, but everyone else plays the same thing except for the last measure.
I currently have placed the 1. and 2. lines on the last measure only, and have only written the first horns line. I obviously have to undo that repeat and write it out fully, or I won't have anywhere to write the notes. But that means that the other musicians will find themselves with a bunch of useless measures.
So, is this something one must just change separating and printing out the parts? Manually deleting the superfluous measures and adding the repeats?