Resizing SketchRenderer?

Is there a clean way to resize a sketchrenderer so it only draws to part of the display?

        cam.setFrustumPerspective(55.0f, width/2f /(float)height, 1, 1000);
        cam.resize(width, height);
        cam.setViewPort(0.0f, (float)Math.sqrt(0.5), 0.0f, 1.0f);

I had to play around with this forever just to get to that point.  I wanted it to take only half the width of the viewport (320 out of 640) but it kept coming out all distorted.  Eventually I figured it out that it fills the viewport dimensions given, but then within that viewport it draws the actual scene as if the edge of the viewport was 1.0... so basically that's where the square root comes in.  I needed the number that when you multiply it by itself it gives you 0.5.  But I'm still left with that extra bit on the edge.

There has got to be a better way, but I looked at the sketchrenderer code and tried changing the values for the fullscreenQuad but nothing made any difference at all.  I tried changing the display width via display.setWidth before rendering and got nowhere as well....

So, what should I do?

There's no clean way to do this… You can re-write a lot of code and have things work, or you can hack and have things work, also…

Make this a suggestion for jME 2.0.

Hmm well could I mask out the other half somehow?  Then I could draw the right half by masking out the first half…

As far as band-aid fixes, what's the easiest way to clear only part of the backbuffer?