usesrcdim equivalent with opengl slabs?

I made a little jitter hack that makes a movie into horizontal lines just by changing the srcdim for the matrix. I want to apply this effect to incoming opengl textures. Is there a similar trick I can do with slabs so I don't have to waste CPU rendering to a matrix?

Here is the original patch with matrices:

Edit: On a similar note, how can I use slab processing to change color information such as hue, saturation and brightness? It seems like it should be simple but I'm having a hard time finding information on the various effects you can do with slabs.