I haven't tried it but I've considered it. It seems to me that you'd either need to:
1) Model your columns as finely meshed walls or;
2) Model your columns as diagonal members running between overlap zones.
The point being that I don't think that modelling the columns using vertical line elements would produce the diaphragm forces that you're looking to capture.
I'm curious to see how this works out for you.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
In order to keep it simple, I would try to model a frame element of an assumed effective width (say 8') and get the forces on that discrete element. In order to get the moment due to eccentricity, you would have to model a "rigid" link supporting the walking column. I have done (2) as KootK suggests and designed the transition reinforcement. A simple check would a T/C check based on the floor-to-floor height, but if that is too conservative, you might consider additional diaphragms.
I have tried modelling the columns as walls. I am taking the shear force at the transition level as the diaphragm force at that level, though another engineer at my work suggests we should be taking the shear difference between this level and the level below. This would give me a lower diaphragm force.
