Yay!! the 300 Christmas card order is finished. You might have read about it here.
Thanks for all the helpful comments I received. Someone suggested changing the printer settings so that not so much ink was laid down on the card, but I'd already tried that - it gave a far inferior print of the photo.
So I've spent the last four days feeding the printer individually and spreading the cards everywhere possible! And then each one had to fed through the printer again to print a logo on the inside.
I thought of using fixative, but didn't think the quantity involved would be good for my lungs and it's not the sort of weather when the window or door can be open. So in the end I layered a piece of paper between each one when the inside had been printed, just as a safeguard against any smudging.
They're all done ahead of deadline, so I'm pleased.