so I kinda figured out an ugly workaround that gets the desired result.

1) Mute the offending soloist track in the style
2) Shift+f4 to open the Select Soloist dialog
3) Search for the soloist that you muted in step 1)
4) Choose Custom options to set the chorus start and # bars

There you go, now you have 2 soloists, but the obnoxious one that refused to stop playing is now banished to the parking lot.