Could you
Could you show an example picture ?
How did you make/test it ?
At here
Editing the neon-plasma-glow-by-FRUiT plasma/desktop theme /widgets/panel-background.svgz picture file. Disabling the object fill -> full transparent panel.

I can't see panel shadows.
Take 2
KDE documents:
From the Kubuntuforums:
The original Air theme (1), Transparent (2), Without the shadow (3).

1) Copying the default plasma theme (Air) from the /usr/share/kde4/apps/desktoptheme/default to the ~/.kde/share/apps/desktoptheme/transparent .
2) Editing the ~/.kde/share/apps/desktoptheme/transparent/metadata.desktop. Changing the theme name to the Transparent
3) Editing the ~/.kde/share/apps/desktoptheme/transparent/translucent/widgets/panel-background.svgz

4) Changing the Fill from the Linear gradient to the No Paint. The result is a transparent panel with the shadow (2)

5) Removing the shadow. Picking the shadow elements and deleting them. The result is a transparent panel without the shadow (3)

6) If you want to use the partial/mini panel edit the mini elements. Change the Fill to the No Paint.

The panel svg image is a bit bare....
