One staff of system should play only 2nd pass of repeat

I am creating rehearsal files for our next concert. My process includes transcribing from sheet music into MuseScore and then exporting mp3 files. I am stuck on an unusual repeat problem with "Play for Me a Simple Melody," as attached.

As you can see in the score on page 1, a repeat begins in measure 5. The repeat ends on page 3 at measure 20, with measure 20 playing only on the 1st ending. This would be trivial, except the staff labeled "Part I" is annotated to play "2nd time only." I can't get this to play correctly for my rehearsal files without expanding the repeat with additional measures.

I am attaching a very simple 4-measure test case with a repeat for measures 2-3, and measure 3 being a 1st ending. The test case is much shorter than the original score, but exactly recreates the problem. If I get a solution for the test case I can apply it to the original score.

The puzzle -- (Your mission if you choose to accept it) -- is to figure out how to treat test case measures 2-3 as rests for Part I during the first pass of the repeat, playing both parts on the 2nd pass, and maintaining measure 3 as a 1st ending, without adding any measures.