I think the only way in the current ArtRage is to duplicate the layer enough times, and then erase everything you don't want on each layer.
As I've mentioned before, I often forget to make a new layer when I start up ArtRage for a new painting, and then am disappointed when I want to do a background (or something underneath). Turns out you can duplicate the layer, clear the bottom layer, and then set the paper type to 'Cel' (which is transparent) on the duplicated layer.
I was initially unhappy that there was no selection tool in ArtRage, but I think maybe now it was to intentionally make it more of a natural media toolbox. You can't really copy and paste with real oil-paints :-)
In any event, if it's not there in ArtRage 3 I'll be happy. I've still got Pixelmator for any photo-editing-type work I need to do.
WARNING: ArtRage can cause serious loss of time, and excessive smiling! Use with care! Frequently!
“All creativity is an extended form of a joke.” – Alan Kay