Can a contact have multiple roles with a customer?

I have a situation where I have contacts that are associated with multiple customer/companies.  And, at a particular customer/company I want to give them more than one "contact role".  As an example, let's suppose I have a contact named John Smith who is affiliated with Company A and Company B.  At Company A he is "CFO" and at Company B he is "Controller".  Now I want to give John Smith a secondary role at Company A "Board Member". 

I don't want to create combo contact roles as this will get unwieldly.  What I'd like to do is create a custom field in the contacts record called "secondary role".  But I need this field to be unique for the contact at each customer the contact is associated with.  In other words, when I set the secondary contact field for John Smith to Board Member, I only want that associated with his record for Company A not Company B.