Hi Zedd,
This is mostly already possible.

Look for the "Held' checkbox in the RealTracks Picker, it's near the top-right, near the Bluesy, Simpler, and Direct Input checkboxes.
If you check that box when choosing a RealTrack, it'll hold every chord. This won't tell it to play a hold on each bar though, unless you enter one chord per bar.
Thanks
Kent
PG Music