Some others and myself requested this save, months ago, and no one stepped up to the plate, so for the last couple of days I went about doing it, which took a long time and it kind of sucked a lot.
This won't get you any difficulty achievements (if there are any for this DLC, I can't remember) because it was done on novice.
Attached is a rar holding an autosave in the void level (where you have to replace the painting). So pop it into a thumbdrive and play off that.
I'm not sure if the autosave is before or after collecting the painting, but really it doesn't matter. I have blink maxed out as the bottom button (if it's not on that button already), just blink over to the replacement painting and then bring it back. When the witch isn't looking drop down in front of the painting and replace it then hop back above it and simply wait for a little bit. I ended up with around 70-80 coin more than required, so yay I guess.
Enjoy your free 70 gamerscore. :-D