Line reference mandatory for Returns

Hi, somebody has applied a customization to make mandatory the line reference only for returns ?

i´ve tried setting as required the Reference Type of Additional Line Return Information in Descriptive Flexfield Segments but it applies for all lines including for a Sales order Entered directly on sales order form

I´ve tried too with some code on custom code but without success, i will apreciate any tip can you give to me.

many thanks.