Defult values for Order ATTRIBUTE values

 Hi, I need some help, When i am selecting the Customer Number  in Sales Order screen, i want to populate the some additional values in Attributes against current customer. I can do from CUSTOM.pll but once i am opening DFF form once i select Context, i am not able to see the attributes values which are populated from CUSTOM.pll. Then i realized once we selecting the Context, it is clearing the attribute values, and placing the default values from which we defined at Descriptive Segments level, I am not sure ... Even i am not able to getting exact trigger event for DFF form from Sales Order screen after selecting Context? How can i Populate default values in Attributes when i enter customer number ?