Here's a page from the body manual showing the hold open spring on the bottom of the lower hinge. With the door wide open, maybe it is possible to snap the loop of the spring over the inner tab and then stretch the hook end of the spring over the outer tab? Probably takes two people.
A stout tool will be needed to extend the spring. Something like an ice pick bent into a U-shape at the end. Or a loop of heavy wire that can be cut once the spring is seated.