You need to define a service to run preferably on node 2 with failover to node 1, and give a your batch jobs a connect string that connects to that service:
srvctl add service -d whatever -s batchserv -r node2 -a node1
and in your tnsnames.ora,
I've recorded many demonstrations of this sort thing,
Oracle Certified Master DBA
Thank you John for that quick answer. I'll read some more on Skillbuilders as soon as I have some spare time.
If that is the way to go then I'll investigate further and follow your suggestion.
Should you have any other ideas how to guide package execution to a certain db instance, please let me know.
Another method is to use the old style DBMS_JOB interface to run your PL/SQL code and set the instance parameter (of the Submit() call) to force execution of that job on a specific node.
See DBMS_JOB for details.