I was playing around with Omnisphere and found a nice trick. I set up four harmonia layers, a fifth, a minor third, a fifth and a major third up from the played note. I set their levels to 0 but mapped the first two to key yaw and the other two to key roll, so you can play a single bass note with each key, and then make a major or a minor triad by bending the key.
It works quite nicely, but of course the volume of the chord goes to zero when you release they key, and you can only play one chord at a time. Might be a worthwhile future addition to EigenD to have this kind of playing trigger new midi notes, then it would work with all polyphonic AUs and would let the instrument's envelope generator do its thing instead of manually fading the volume.