Filtered list in relationship tab driven by master list on main form.

Hi, I have a drop down list exposed on the main form on the Simple ECO itemtype. I have another list property defined on the Affected Item itemtype which is a relationship. Based on what is selected in the main form, I would like the list on he Affected Item to be filtered to show only the values relevant to the selection made on the main form. Filtered list don't work very well on a relationship. It would be helpful to get some ideas and probably some pseudo code on how to implement the solution.