I would not advise your end-users adjust this. This is too much to ask them.

The best way to ensure that the viewer is properly cached is to decide upon a particular (stable) version of Omniscope, and either host it yourself, or ask us to "freeze" that version, so your JNLP file can refer directly to it and it does not change for a long period of time.

Unfortunately due to bugs in the past with Java Webstart, we have a number of mechanisms to try and ensure caching happens when desired, but more importantly NOT when NOT desired. This doesn't always work perfectly.