I have tried getting a loose-fitting sleeve to roll down an uplifted arm with no success. We are looking at mesh construction, subdivision, gravity, and outfit friction. If I can figure out the right combination and weight mapping, then it might be possible. But, ATM, no go.

Getting a shirt that shows the midriff while the arms rise appears to be doable. Again, weight mapping and dynamic/constraining controls need to be adjusted accordingly to get the desired effects. As I mentioned before, trial and error and documentation. Chances are, you will immediately forget your workflow as soon as Poser is shutdown.