Events from Editor Controls

I have a simple WebDataGrid that has a drop-down for 'Organization' and a drop-down for 'Roles' in the RowAdding Behaviors.  I would like the drop-down for 'Roles' to change based on the selection in the 'Organization' drop-down and show only the roles that are applicable to that organization.  Is this possible? 

I have a sql datasource for roles with a parameter for organization, but the drop-down is not listed as a control for the parameter.  Thanks for any advice!