I am having the exact same problem. Now I figured out how to mod or mute the left hand voices in OMB ITSELF -- for instance, by simply not enabling the "left hand" Voice 3 and 4 settings. Easy enough.
But what if one is using add-on voices (say from a VST plugin, soundfont, etc.)? If I use a grand piano sample via Forte/LiveSynth for example -- I get the left hand chords in OMB no matter what I set for voices in the program.
Can I set the split differently and silence the left hand in the host itself? Is that what you are referring to above? I am new to all this electronics stuff, forgive the lack of basic knowledge.