Add field to dynamic selection in FBL1N

Below link is quite useful for adding field to Dynamic selection in FBL1N

http://scn.sap.com/thread/3329962

 

Also, Please read SAP note 310886 - Line items: Dynamic selections ignored.
This note explains that only fields from certain tables can be added.
FBL1N only fields from: LFA1, LFB1 and BSIK
FBL3N only fields from: SKA1, SKB1 and BSIS
FBL5N only fields from: KNA1, KNB1 and BSID