How to put the actor on Background like Conky do?

[Mz <mengzhuo1203 gmail com>]

Hi, guys

I had tried creating a new actor(like St.Label) and keep "lower_bottom" in Mainloop to make it done, but such method is silly and ate too much CPU...

I think that the source code of mutter(src/compositor/meta-background-actor.c) said it just put pixmap on BackGroundActor, is there any bypass or override way to add some extra actors(to make some widgets) on the Background?