There's an even better way to do this that doesn't involve any code. There are two steps to take in the CMC (this assumes you're on BI4.0):
1. Under Servers, remove the BI Inbox destination for all AdaptiveJobServers in your system.
2. Under Applications, go to the User Security for BI Launchpad.
- Modify the rights for the Everyone group.
- Go to the Advanced tab and click on "Add/Remove Rights".
- Click on "Application" then "BI launch pad".
- Explicitly deny the right "Send to BusinessObjects Inbox".
Doing this will prevent users from scheduling to their inbox in the first place.
-Dell