Downsample inputs?

is there a way to automatically let let blender downsample the image imputs? 'cause I’m working with >4k exr images, and is a major pita. I got to save them at 1/5th of the original size, make the compositing, then change all the node inputs with the big ones…

Since 2.46 there are the option of Disk Preview Proxies.
You might want to have a look on this feature.
I think you have to add your scene in the Sequence Editor to activate this.
I didn’t try this before, but perhaps it is what your looking for.

Some info:

the only problem is that, since I’m using the node module as a pure compositing app - ie, not using the 3d part of blender, just inputing my images, using nodes to compose them in various ways, and output them… How could I add the node flux to the sequencer? And, even if proxying the images from there, will I have the benefits in the node editor? Thanks!