Wide icons in the panel

[Tim Cuthbertson <tim gfxmonk net>]

I've added an indicator to the panel for my tiling window extension,
and want to have custom icons to represent different states of the
workspace (i.e different layouts).

I'd like to have wide icons, as it gives you a bigger hit target and
is easier to distinguish the layouts visually that way. Is it possible
to use non-square icons in the panel? If not, can I use some other
drawable mechanism? (it doesn't need to be an icon specifically, I
just need some sort of image).

And lastly, can my images live inside my extension directory? If not,
what environment variable should I set so that gnome shell can find
them if I don't install them in the system-wide location?

Thanks,
 - Tim.