No, it's not impossible, it depends on the input sequence.
This works:
|Chord|Dur:4th|Pos:-4,-2|Opts:Stem=Up|Dur2:4th|Pos2:-8
|Chord|Dur:8th|Pos:-4^,-2^|Opts:Stem=Up,ArticulationsOnStem|Dur2:8th|Pos2:-8^
|Chord|Dur:4th|Pos:-8|Opts:Stem=Down|Dur2:4th|Pos2:-4,-2
This doesn't:
|Chord|Dur:4th|Pos:-8|Opts:Stem=Down|Dur2:4th|Pos2:-4,-2
|Chord|Dur:8th|Pos:-4^,-2^|Opts:Stem=Up,ArticulationsOnStem|Dur2:8th|Pos2:-8^
|Chord|Dur:4th|Pos:-4,-2|Opts:Stem=Up,ArticulationsOnStem|Dur2:4th|Pos2:-8
Not easy to detect it in the editor.