Join in VBC based on a Siebel BC.

Hi Team. We have offerinformation in Siebel e.g. name, description, plan code, price, etc. Howeve the offers eligilbe for a customer is recieved from a external system using web service. However this webservice only provides list of plan codes... But we need to display other info like name, desc for the plan codes returned by the service to the user. I though of using VBC and then have a join to a product BC based on VBC field plan code. But it is not working.. Any ideas how we do this in Siebel