Not sure if is this has ever been posted here or not, but we stumbled on this recently:
LatchNVent | Pet Door Prop for Dogs and Cats. It allows you to close and latch a door while still leaving it open a bit. Full details are on the site, and it's only $30 including shipping. I'm sure there are plenty of home made remedies, but this seems to work very well with our Maltipo. Just wanted to pass it on.