JPA - Optional columns

JPA - Optional columns

We have many customers data in separate databases per customer which
should have the same schema/table structures. However there is a table
that has extra columns in some databases compared to others.
For example for customer A there is a table X with columns a, b, c, d. For
customer B there is a table X with columns a, c, d. I need to capture b if
it exists but can ignore it if not.
Is there a way to tell JPA to ignore those columns if they don't exist?
@Basic(optional=true) reads exactly like what I want but the documentation
indicates it is for another purpose.
Currently I get, as expected, Unknown column 'table.field' in 'field list'
P.S. I can't just add the columns to the databases that don't have them
unfortunately.