You mention the Camel JPA binding in the title of your post, but the example provided used Camel SQL. Do you have a requirement to use one or the other?
I have not tested this locally, but it appears the Camel SQL component supports using a header 'CamelSqlQuery' to override the SQL query specified in the endpoint:
What implementation are you using to invoke this reference (Bean, Camel, ...)? If it's a Camel route, then just set the header using setHeader in your route definition. If it's a Bean implementation, then you'll need to use a ReferenceInvoker: