Stacked Poly Chords with complex chords on bottom

Take a look at this chart "Ice Bridges Before Road" http://musescore.com/score/24889
It has stacked poly chords with complex chords on the bottom (instead of just a bass note on bottom).
For example, the first chord on the second line is: C/(Gbadd9), meaning play a C triad in the right hand and a Gbadd9 in the left hand. While these type of chords are uncommon, I would like musescore to display them with a *horizontal* line between the upper and lower chord. My workaround in the chart was to type return after the C, and then the /Gbadd9, but it doesn't look visually pleasing. I am a programmer and would be willing to implement this.