KDocker will help you dock any application in the system tray. This means you
can dock openoffice, firefox, thunderbolt, eclipse, anything!
Just point and click. Works for both Plasma and GNOME (In fact it should work
for most modern window managers that support NET WM Specification.
I believe it works for XFCE, for instance)

All you need to do is start KDocker and select an application using the mouse
and the application gets docked into the system tray.
The application can also be made to dissappear from the task bar.