Security: restrict package access

I would like to restrict package access for the code fragements
compiled and executed by Janino ExpressionParser. The Janino compiled code
should only be able to access methods of the superclass that it
implements and from the java.lang.* package. The methods of that superclass,
that are implemented in my source code, should than be able to call whatever
they want again.

In other words. The thread that executes the JaninoExpressions should
within the Janino Code be restricted to only have access to classes withiin specified
Packages, and as soon as it comes back to my code, the thread should have
full access again.

We use janino to make parts of our application configurable. Without the restriction
this would be a too big security breach.

Some keywords i have been googling but without much success:
- ProtectionDomain
- checkPackage
- SecurityManager
- SandBox
- sealed package
but I did not manage to achieve anything.

Is it doable at all. Any hints or even example code snappets?

Thx