Semi,
I play guitar also and I know what you mean about lowering the low E-string to D to get a full D chord effect with regular tuning. Your talking about playing in the key of D I assume. It makes playing a full G chord a challenge though. I play Country Road and Rocky Mountain High that way. Maybe others, I forget.
I'm not sure how to get that sound on a keyboard. Maybe if you Split the keyboard to have a left hand bass sound and play left hand chords in a low root position(full or cheat) you can get that sound somewhat. You don't get the sympathetic string ringing but at least it's a full chord with a deep bass note. Hope that made sense.