Hasta La Motion!

Newbie question here, bear with me.
Lets say I have a 720p image in Nuke and I want to downsample this, so the image becomes pixellated much like the downrez option in Nuke, but then render this out with its initial spatial resolution of 720p.

How would one go about doing this. I have tried using a reformat node to specify a lower res and then I have tried stretching this back up with the scale option in the transform node, but the image retains its initial 720p quality. I want to render out with the same spatial resolution but fill it with a downsampled version of the original image.

I hope someone can help.
Thanks
Marmalade