JPA is for OO programs which need a OO view of persistence storage.
if you want exact resultSet then JPA is not much a good choice for you.
for example if you want feed this result into a report or OLAP software, which user creates a SQL to run you may prefer to bypass JPA
please refer to "Fast Lane Reader" pattern
in such a cases create a "Session Facade" for this set of queries  that runs all "Stored Procedures" and "Native Queries" with special set set of columns in result set.

I agree you about JPA and we use JPA (Hibernate 3) for this purpose. these queries
that I have to run natively are about only 5% of all persistence layer but they are exist
and I can't find a way to run them with JPA/Hibernate. Now I am working on a solution
that someone suggessted on the web and if it was correct and helped I will tell about
that.