See also
http://pve.proxmox.com/wiki/Java_Console_(Ubuntu)
Why is installing a package a "pain"? The Oracle Java is available on all platforms, easy installation in a few minutes.
BTW, are you sure that the problem is on the VNC java code and not on the OpenJDK browser plugin? As the console works great on Oracle Java, probably the issue is on the other side?
In contrast, the spice plugin for browser is not yet available on all platforms/browsers and all this is unstable/experimental code. I would like to have spice running but for managing servers the VNC console is also great. (virtual desktops is another story).