Make part of the GUI become invisible

I have a stage select on my game, and I want to add arrows that slide them.

Picture this:

<-   |[Stage1]|  |[Stage2]|  |[Stage3]|   ->

I want to make it so that when you slide it right:

<-   ge1]|  |[Stage2]|  |[Stage3]|  |[S   ->

It looks like this, cutting off the left side of the stage 1 button and a portion of the right side appears.

Now I realise this could be easily achieved by putting a texture on a higher layer on the sides like

|LAYER|ge1]|  |[Stage2]|  |[Stage3]|  |[S|LAYER| 

And then put the arrows on the layer, however, I want the GUI to be rendered on the actual background of the game, so putting layers on would make me have to make a whole 2D screen, when currently my GUI overlays the 3D background.

So essentially, what I’m asking is, is there a way to either “cut” into the left and right side of the things as they move, or (more ideally) make a transparent GUITexture that tells everything underneath it to be transparent too?

Thanks

I just thought:

How about as a solution, using two cameras. Would this be possible in Unity Free? What I’d need is one normal camera with the GUI arrows on it and then a second camera with the stages on it, but that camera would take up less of the screen.

Like

-----------------------------------------------
|      |                               |      |
|      |          Camera2 Span         |      |
|      |<----------------------------->|      |
|      |                               |      |
|      |                               |      |
|  <-  |AGE1     STAGE2     STAGE4    S|      |
|      |                               |      |
|      |                               |      |
|      |          Camera1 span         |      |
|<------------------------------------------->|
-----------------------------------------------

Is this possible in Unity Free?