How do I change the default value of the “position” category attribute?

Question

I would like to update the default position value that products are assigned when they are added to a category. When you update a category from the categories editor, new products are saved with a position of 0. When you add a product to a category via the tree when filling out the product, it saves with a position value of 1.

What I want to do is have items save with a position of 100 instead of 1.